The Response Of Nuthatches (Sitta Spp.) To Restorative Treatments
In Ponderosa Pine Ecosystems Of Northeastern Oregon

Christine A. Rothenbach
B.Sc., Arizona State University, 2000

Thesis Submitted in Partial Fullfillment
The Requirements For The Degree Of
Master Of Science
in
Natural Resources and Environmental Studies
(Environmental Science)

The University Of Northern British Columbia
March 2007

© Christine A. Rothenbach, 2007

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Abstract
Ponderosa pine (Pinus ponderosa,) forests in western North America are in need o f
restoration due to the impacts offire suppression. The effects o f different restorative
treatments on avian species should be determined before these treatments are widely applied.
O f the common resident passerines in ponderosa pine forests, three species are nuthatches
fSittaj. These nuthatches have similar ecological niches to each other but different life
history traits. The objectives o f this research were to determine differences among treatments
in: abundance andforaging behavior o f Pygmy f'Sitta pygmaeaj, White-breasted (S.
carolinensisj, and Red-breasted (S. canadensis,) Nuthatches, and daily nest success o f Pygmy
and Red-breasted Nuthatches. Structural characteristics o f trees usedfor foraging and
nesting were also documented. Thinning ( ‘thin )’, prescribed burning ( ‘burn j, thinning
followed by burning ( ‘thin and burn j and ‘control’ areas were used. Pygmy Nuthatches
were observed more often in ‘thin and burn ’ areas than in ‘thin ’ or ‘burn ’ areas. White­
breasted Nuthatches were encountered more often in ‘thin and burn ’ units than ‘control ’
units. The abundance o f each species o f nuthatch in treatment areas did not seem to be
dictated by tree structural characteristics alone. Red-breasted Nuthatches spent more time
foraging on trees in ‘thin and burn ’ areas than in ‘thin ’ or ‘control’ areas, but this difference
was not due to tree structure. Red-breasted Nuthatches foraged upon Douglas-fir
(Pseudotsuga menziesiij more than it was randomly available, and used trees fo r foraging
that were larger and had less live crown than trees not used. White-breasted Nuthatches
foraged on trees that were larger and had less live crown than average. Pygmy Nuthatches
were more likely to forage on trees that were large in diameter. Models using structure and
microhabitat o f nest trees performed poorly at predicting the success o f nests o f Pygmy and
Red-breasted Nuthatches. The number o f nests o f Red-breasted Nuthatches was different
among treatments, with fewer nests within ‘thin and bum ’ treatments than expected. The
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number o f snags available fo r nesting was also different among treatment types, with ‘burn ’
units having more and ‘thin and burn ’ units having fewer snags than expected. More snags
surrounded nest trees o f Red-breasted Nuthatches, and snags used fo r nests had less canopy
cover than snags not used. Snags used fo r nesting by Pygmy Nuthatches were larger in
diameter than snags that were not used. The restorative treatment that combined thinning
and burning appeared to improve habitat suitability fo r both White-breasted and Pygmy
Nuthatches, while Red-breasted Nuthatches appear to be resilient to treatment type.

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Table of Contents

ABSTRACT................................................................................................................................... II
TABLE OF CONTENTS...........................................................................................................IV
LIST OF TABLES......................................................................................................................VI
LIST OF FIGURES................................................................................................................ VIII
ACKNOWLEDGMENTS..........................................................................................................IX
1. GENERAL INTRODUCTION............................................................................................... 1
1.1. T he R ecent H istory of P o ndero sa P ine F orests within W estern N orth
A m e r ic a ..........................................................................................................................................................1
1.2. N uthatches a n d O ther P rim ary C a vity - excavating B irds are Im portant to
M a inta in within P on derosa P ine E c o s y s t e m s ............................................................................3
1.3. P revious R esearch on the E ffects of Resto ration Treatm ents o n C a v it y nesting B i r d s ............................................................................................................................................ 11
1.3.1. Silvicultural T h inn ing.............................................................................................................. 11
1.3.2. Understory B u rn in g..................................................................................................................14
1.3.3. Restorative T reatm ents............................................................................................................15
1.4. H u ng ry B ob S tu d y S ite a n d R estorative T r ea t m en t s ................................................16
1.4.1. Hungry B o b .................................................................................................................................16
1.4.2. Restorative T reatm ents............................................................................................................18
1.5. T hesis O bjectives : D eterm ining the E ffects of R estorative T reatm ents on
N uth a t c h e s ................................................................................................................................................19

2. THE EFFECTS OF RESTORATIVE TREATMENTS IN PONDEROSA PINE
(PINUS PONDEROSA) ON THE FORAGING ECOLOGY OF NUTHATCHES
(SITTA SPP.) IN NORTHEASTERN OREGON..................................................... 22
2.1. A b s t r a c t ............................................................................................................................................22
2.2. Intr o d uc tio n .................................................................................................................................... 23
2.3. M e t h o d s .............................................................................................................................................24
2.3.1. Study S ite .................................................................................................................................... 24
2.3.2. Treatments and Study U n its.................................................................................................. 24
2.3.3. Foraging E c o lo g y ..................................................................................................................... 25
2.3.3.1. Foraging B eh a v io r ........................................................................................................... 25
2.3.3.2. Structural Characteristics o f Trees U sed for Foraging.......................................... 29
2.3.4. A n alysis........................................................................................................................................29
2.3.4.1. U se o f Treatment Units by B ird s.................................................................................29

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2.3.4.2. D iffering U se o f Trees A m ong Treatment T y p es................................................... 31
2.3.4.3. Structural Differences A m ong Trees W ithin Each Treatment U n it ................. 35
2.3.4.4. Behavior Differences A m ong Treatment U n its.......................................................36
2.4. R e s u l t s ............................................................................................................................................... 38
2.4.1. U se o f Treatment Units by B irds..........................................................................................38
2.4.2. D iffering U se o f Trees betw een Treatment U n it s .......................................................... 40
2.4.3. Structural D ifferences A m ong Trees W ithin Each Treatment U n it.......................... 50
2.4.4. Foraging Behavior D ifferences betw een Treatm ents.................................................... 50
2.5. D is c u s s io n ......................................................................................................................................... 54

3. THE EFFECTS OF RESTORATIVE TREATMENTS IN PONDEROSA PINE ON
NESTING ECOLOGY OF RED-BREASTED (577 74 CANADENSIS) AND
PYGMY (SITTA PYGMAEA) NUTHATCHES.........................................................60
3.1. A b s t r a c t ............................................................................................................................................60
3.2. In tr o d uc tio n .................................................................................................................................... 61
3.3. M e t h o d o l o g y ..................................................................................................................................62
3.3.1. Study S ite .................................................................................................................................... 62
3.3.2. Treatments and Study U n its.................................................................................................. 62
3.3.3. N est-site Preferences................................................................................................................ 63
3.3.4. A n alysis........................................................................................................................................66
3.4. R e s u l t s ............................................................................................................................................... 68
3.5. D is c u s s io n ......................................................................................................................................... 77

4. GENERAL DISCUSSION.....................................................................................................86
4.1. T he E ffects of Restorative T reatm ents w ithin P on derosa P ine on
N u th a t c h e s ............................................................................................................................................... 86
4.2. F uture R e s e a r c h ........................................................................................................................... 87

LITERATURE CITED.............................................................................................................. 89

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List of Tables
Table 2.1. Classification of nuthatch behaviors observed (based on Remsen and Robinson
1990)..................................................................................................................................31
Table 2.2. Height categories recorded from each tree foraged upon by nuthatches................ 34
Table 2.3. Candidate models to predict the number of seconds that Red-breasted Nuthatches
foraged upon each tree using treatment and tree structure............................................37
Table 2.4. Candidate models to predict the number of seconds that White-breasted
Nuthatches foraged upon each tree using treatment and tree structure........................37
Table 2.5. Candidate models to predict the structural characteristics of trees that nuthatches
foraged upon..................................................................................................................... 40
Table 2.6. Zone combinations used to compare nuthatch foraging along horizontal and
vertical axes...................................................................................................................... 43
Table 2.7. Amount of time (minutes) birds were observed foraging in each treatment type..45
Table 2.8. Comparison of models using the structural characteristics of trees to predict the
length of time Red-breasted Nuthatches foraged upon them.........................................50
Table 2.9. Parameter estimates of each variable within the best performing model using the
structural characteristics of trees to predict the length of time Red-breasted
Nuthatches foraged upon them........................................................................................50
Table 2.10. Comparison of models using the structural characteristics of trees to predict the
length of time White-breasted Nuthatches foraged upon them.................................... 53
Table 2.11. Parameter estimates of each variable within the best performing model using the
structural characteristics of trees to predict the length of time White-breasted
Nuthatches foraged upon them........................................................................................53
Table 2.12. Information criteria of candidate models used to predict the structural
characteristics of trees foraged upon by Pygmy Nuthatches........................................55
Table 2.13. Parameter estimates of each variable within the best performing model using the
structural characteristics of trees to predict foraging use of Pygmy Nuthatches
55
Table 2.14. Information criteria of candidate models used to predict the structural
characteristics of trees foraged upon by Red-breasted Nuthatches............................. 58
Table 2.15. Parameter estimates of variables within the best-performing model using the
structural characteristics of trees to predict foraging use by Red-breasted Nuthatches
........................................................................................................................................... 58
Table 2.16. Information criteria of candidate models used to predict the structural
characteristics of trees foraged upon by White-breasted Nuthatches..........................60
Table 2.17. Parameter estimates of each variable within the best performing model using the
structural characteristics of trees to predict foraging use by White-breasted
Nuthatches........................................................................................................................ 60
Table 2.18. Differences in vegetation structure among treatment types................................... 62
Table 2.19. Results of Mann-Whitney U-tests used to compare the amount of time that
Pygmy Nuthatches spent foraging with different zones among treatments................. 64
Table 2.20. Results of Kruskal-Wallis H-tests used to compare the amount of time that Red­
breasted and White-breasted Nuthatches spent foraging with different zones among
treatments.......................................................................................................................... 64
Table 3.1. Candidate models to predict the structural characteristics of snags that nuthatches
nested within..................................................................................................................... 79

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Table 3.2. Information criteria of candidate models used to model daily nest survival of Re­
breasted Nuthatches within Hungry Bob........................................................................81
Table 3.3. Parameter estimate, standard error, and 95% confidence intervals of nest-tree
structural variables in predicting daily nest survival for Red-breasted Nuthatches.. ..81
Table 3.4. Information criteria of candidate models used to model daily nest survival of
Pygmy Nuthatches within Hungry Bob.......................................................................... 85
Table 3.5. Parameter estimate, standard error, and 95% confidence intervals of nest-tree
structural variables in predicting daily nest survival for Pygmy Nuthatches.............. 85
Table 3.6. The number of snags within decay classes 2, 3, or 4 and over 11 cm in diameter
within each treatment type............................................................................................... 90
Table 3.7. Information criteria of candidate models to predict the structural characteristics of
snags that Red-breasted Nuthatches nested within........................................................ 92
Table 3.8. Parameter estimate, standard error, and significance of nest-tree structural
variables in predicting which snags were used for nesting by Red-breasted
Nuthatches......................................................................................................................... 92
Table 3.9. Information criteria of candidate models to predict the structural characteristics of
snags that Pygmy Nuthatches nested within...................................................................93
Table 3.10. Parameter estimate, standard error, and significance of nest-tree structural
variables in predicting which snags were used for nesting by Pygmy Nuthatches 93

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List of Figures
Figure 1.1. Distribution of ponderosa pine within western North America...............................2
Figure 1.2. Distribution of Pygmy Nuthatch within western North America............................5
Figure 1.3. Distribution of White-breasted Nuthatch within western NorthAmerica............... 7
Figure 1.4. Distribution of Red-breasted Nuthatch within western North America................. 9
Figure 1.5. Hungry Bob location within northeastern Oregon.................................................. 19
Figure 2.1. Foraging zones within a typical ponderosa pine..................................................... 33
Figure 2.2. Number of nuthatches encountered within each treatment type............................47
Figure 2.3. Mean rank of time (seconds) each nuthatch species spent foraging upon each tree
within each treatment type............................................................................................... 49
Figure 2.4. Mean amount of time (natural log of seconds) that Red-breasted Nuthatches were
predicted to forage upon trees within each treatment....................................................52
Figure 2.5. The probability that Pygmy Nuthatches would use a tree for foraging increased as
the diameter (cm) of the tree increased........................................................................... 56
Figure 3.1. Example of a typical nest observation site on the Hungry Bob research units.. ..76
Figure 3.2. Daily nest survival of Red-breasted Nuthatches tended to increase as diameter
increased............................................................................................................................82
Figure 3.3. Daily nest survival of Red-breasted Nuthatches tended to increase as nest height
increased............................................................................................................................83
Figure 3.4. Daily nest survival of Red-breasted Nuthatches tended to increase as canopy
cover increased................................................................................................................. 84
Figure 3.5. Daily nest survival of Pygmy Nuthatches tended to decrease as canopy cover
increased............................................................................................................................86
Figure 3.6. The number of Red-breasted Nuthatch nests found within each treatment type and
each year............................................................................................................................88
Figure 3.7. The number of Pygmy Nuthatch nests found within each treatment type and each
y e a r.................................................................................................................................... 89
Figure 3.8. The probability of a snag being used for nesting by Pygmy Nuthatches increased
as snag diameter increased............................................................................................... 94

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Acknowledgments
I would like to thank Chris Opio. He always had support and encouragement for me,
and always had a smile on his face. He was an excellent academic supervisor, and one of the
nicest people I have ever had the pleasure of knowing. I would also like to thank Ken Otter.
Besides providing lots of feedback on multiple drafts of this thesis, Ken provided me with
valuable training in the handling and banding of birds. He spent considerable time and
showed considerable patience in securing my first banding sub-permit so that I could band
nuthatches in Oregon. Also I would like to thank Russ Dawson for providing me with much
needed feedback (especially with regards to statistical analyses and interpretation!) and
guidance..
Kerry Farris gave me my first wildlife job, trapping small mammals in Sequoia
National Park. Next, she gave me my first bird job, at the Hungry Bob study site in Oregon.
Then, she encouraged me to apply to UNBC in pursuit of a master’s degree, and helped me
write my entrance proposal. After all that, she has become a good friend. She continues to
be a constant source of encouragement and inspiration. Thanks for everything, Kerry. And I
hope to see you in Bend real soon!
While working with small mammals in Sequoia National Park, I became more and
more fascinated with the birds that I heard all around me. They were made more mysterious
by the fact that you could rarely see them in the tall trees, except as silhouettes against the
sky. Adam Patterson took me out into the forest one day, after unrelenting requests, and
began to teach me the art of identifying birds by their songs and calls. The first bird I learned
from him was the Red-breasted Nuthatch. My hunger for knowledge of all things birdy has
been insatiable since then, but the Red-breasted Nuthatch still embodies that original sense of
fascination and discovery from Sequoia National Park.
To the people that had to learn to deal with my obsession for small bark-gleaning
birds day after day in the field: Regina Wasson, Colin Talbert, Evan Rehm, Tami Brunk,
Rob Spaul, and Brian Bielfelt, thanks. Also, to Jennifer Kapp, who helped me gather my
data and perhaps even developed a nuthatch fixation herself, if just for the summer, thanks
for all of your hard work, accurate data, and all the fun we had with our ‘nuthatch humor’.
You really got me through the frustrations that we shared in an ‘o ff year for nuthatches at
Hungry Bob, mostly with humor, as we entertained ideas about the new species of groundnesting nuthatch we must have discovered in the summer of 2004.
Thanks to my parents. Throughout my life, they both encouraged me to do whatever
I thought would make me happy. Even when that involved horse training, and especially
when I decided to give up equine for avian. I hope you know that this path has truly made
me the happiest I’ve ever been.
No research can be completed without funding. For this important aspect, I would
like to thank the Wildlife Conservation Society, New York, NY; and the Wallowa-Whitman
National Forest Service in conjunction with the Fire-Fire Surrogate Study, which is in turn
supported by the USGS.

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1. General Introduction
1.1. The Recent History of Ponderosa Pine Forests within Western North America

Ponderosa pine (Pinus ponderosa) occurs within the western portion of the United
States and Canada (Fig. 1.1). Historically, frequent fires maintained stands of large, widely
spaced trees on dry, mid-elevation slopes. Since European settlement of western North
America, and especially since 1910, fires were excluded from most of these forests. Forests
affected by fire exclusion were more dense and uniform in their stem dispersion (Mast et al.
1999) with fewer large old trees and more small young trees (Swetnam 1990, Mast et al.
1999). Currently, ponderosa pine forests have higher mortality of old-growth trees, more
stems of shade-tolerant species such as Douglas-fir (Pseudotsuga menziesii) and true firs
(Abies spp.), less diversity within the understory, and more fire-fuels than their pre­
settlement counterparts (Swezy and Agee 1991, Covington and Moore 1992, Mutch et al.
1993, Agee and Maruoka 1994, Harrod et al. 1998). These changes in forest composition
and structure shifted the fire regime from frequent understory fires to infrequent, crowning
wildfires to which ponderosa pine and the organisms associated with them have not adapted
(Agee 1996).
Between 1991 and 2001, approximately 200,000 ha of habitat historically dominated
by ponderosa pine within the Malheur, Umatilla, and Wallowa-Whitman National Forests of
Oregon and Washington was destroyed by wildfire (J. Mclver, Forest Ecologist, USGS, Pers.
comm., 2003). There are an estimated 1.2 million ha of ponderosa pine forest in the Blue
Mountains of Oregon and Washington that need restoration treatment (Caraher et al. 1992).
Within the western portion of the United States, an additional 28 million ha of forest is in
need of restoration (Schmidt et al. 2002, Brown et al. 2004).

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Pinus ponderosa
<«

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SCAtE 1: 15000000

(=c:

100

Figure 1.1: Distribution of Ponderosa Pine within North America. Dark grey areas
represent forests containing ponderosa pine. Reproduced for use within this thesis with
permission from the United States Geological Survey.

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Mechanical thinning and prescribed burning are the most common methods of
restoring fire-suppressed forests to their historic conditions (Agee and Maruoka 1994, Hayes
et al. 1997, Ottmar and Sandberg 2001). These treatments have both been responsible for
decreasing fire intensity after they were applied to ponderosa pine forests (Pearson et al.
1972, Pollet and Omi 2002). Restoration methods will vary according to the extent of
deviation from reference (historic) conditions, and other factors such as economic interests
and climate change (Moore et al. 1999). As early as the 1930s, research suggested that the
exclusion of fire from forests was detrimental to avian species (Stoddard 1931). However,
the effects of various restorative treatments within ponderosa pine forests on biological
aspects of ecosystem function, such as avian foraging and nesting dynamics, are poorly
understood.
1.2. Nuthatches and Other Primary Cavity-excavating Birds are Important to Maintain
within Ponderosa Pine Ecosystems
Three species of nuthatch (Sittidae) are present within the Blue Mountains of Oregon:
White-breasted (Sitta carolinensis), Red-breasted (S. canadensis), and Pygmy Nuthatch (S.
pygmaea). Each has a different association with ponderosa pine, and each has slightly
different foraging and nesting requirements. The Pygmy Nuthatch occurs only in western
North America, and roughly only where mature ponderosa pine and Jeffrey pine (Pinus
jeffreyi) forests occur (Fig. 1.2; Diem and Zeveloff 1980, Szaro and Baida 1982, Baida et al.
1983, Bock and Fleck 1995, Csuti et al. 1997, Gardali et al. 1999, Kingery and Ghalambor
2001). Though more restricted in their habitat than other western North American nuthatches,
Pygmy Nuthatches are the most diverse in their placement of nests (McEllin 1979). They
excavate their nests or use natural cavities more often than they use nest-sites that were
excavated by other species (McEllin 1979, Brawn 1987).

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Figure 1.2: Average number of Pygmy Nuthatches counted per survey route between
1994 and 2003 within North America. From the Breeding Bird Survey, Sauer et al.
2005. The uniform grey area to the north was not surveyed.

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The Pygmy nuthatch is considered an excellent indicator of the health of the avian
community within ponderosa pine ecosystems because of its reliance on mature,
heterogeneous stands (Diem and Zeveloff 1980, Szaro and Baida 1982). Pygmy Nuthatches
may have developed fire-dependent foraging or nesting strategies owing to their near
exclusive residence within ponderosa pine ecosystems (Kingery and Ghalambor 2001). There
is a general belief that the Breeding Bird Survey (BBS) fails to effectively quantify Pygmy
Nuthatch populations (Sauer et al. 1999, Altman and Bart 2001). The BBS is a major tool
used to detect trends of decline in many bird species. For this reason, the Pygmy Nuthatch is
listed as a sensitive species in the Blue Mountains of Oregon based on the decrease of mature
ponderosa pine forest in those areas (USDA Forest Service 1996; Oregon Department of Fish
and Wildlife 1997, US Fish and Wildlife Service 2002). It also appears on conservation
watch lists in Colorado (Webb 1985), Idaho (Idaho BLM 2003), Montana (Clark et al. 1989),
and Wyoming (Clark et al. 1989, Luce et al. 1997). Wisdom et al. (2000) recommend
restoring the dominance of ponderosa pine where it has been taken over by Douglas-fir and
true firs, in order to protect populations of Pygmy Nuthatch from further habitat loss.
White-breasted Nuthatches are also closely associated with ponderosa pine.
However, they breed in good abundance within oak-dominated (Quercus spp.) stands as well
as mixed-conifer stands where either pine or oak are available (Fig. 1.3; Bent 1964, Garrett
and Dunn 1981, Root 1988, Matthysen 1998). White-breasted Nuthatches have been known
to nest more often in natural cavities than excavated cavities in ponderosa pine (Brawn and
Baida 1988a, McEllin 1979), and have only rarely been known to excavate their own nests
(Bent 1964). Red-breasted and White-breasted Nuthatch populations appear to be increasing
within the western United States and Canada. Most of this increase is due to both

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Figure 1.3: Average number of White-breasted Nuthatches counted per survey route
between 1994 and 2003 within North America. From the Breeding Bird Survey, Sauer
et al. 2005. The uniform grey area to the north was not surveyed.

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species extending their ranges northward (DeSante and George 1994, Root and Weckstein
1994). This general increase in population size has masked the general trend of both species
to decline within specific ecosystems, such as Douglas-fir in the northwest and ponderosa
pine in the southwest (Hejl 1994), particularly in California, Colorado, and Oregon
(Ghalambor and Martin 1999).
Red-breasted Nuthatches are habitat generalists. They are present in most forests
within western North America (Fig. 1.4), including populated areas (Rohila and Marzluff
2002) and forest patches (McIntyre 1995). They tend to prefer mixed forests with a fir,
Douglas-fir, or spruce (Picea spp.) component (Ghalambor and Martin 1999, Hobson and
Bayne 2000). Red-breasted Nuthatches will most often excavate their own cavity; however,
they will also nest in boxes, woodpecker cavities, and natural cavities (Ghalambor and
Martin 1999, Aitken et al. 2002). Red-breasted Nuthatches tend to be more common within
old-growth stands than either mature or young forest (Mannan et al. 1980, Carey et al. 1991,
Hannon 2000).
The number of species dependent upon tree cavities best illustrates the value of
cavities. Of all usurped nests reported in the literature, almost 91% were either cavity or
enclosed nests (review in Lindell 1996). Cavity-excavating birds such as nuthatches provide
nesting and roosting habitat for over 60 other bird and mammal species in the Pacific
Northwest region of the United States (Thomas et al. 1979, Brown 1985). Over 25% of
forest-dwelling mammals in the Pacific Northwest use cavities for nesting or resting (Bunnell
et al. 1999). Each excavating species tends to create cavities with different qualities (i.e.
depth, entrance width, volume, height on bole, distance to forest edge, decay type and
extent). Therefore, the diversity of cavity-excavators can influence the diversity of

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Figure 1.4: Average number of Red-breasted Nuthatches counted per survey route
between 1994 and 2003 within North America. From the Breeding Bird Survey, Sauer
et al. 2005. The uniform grey area to the north was not surveyed.

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secondary cavity-nesters in an ecosystem (Brawn and Baida 1988a). Nuthatches, especially
the Red-breasted Nuthatch, might be underestimated as cavity-creators. Within the boreal
forests of British Columbia, cavities created by Red-breasted Nuthatches were used more
often than those of any other excavating bird except Three-toed Woodpeckers (Picoides
tridactylus, Aitken et al. 2002). Nuthatches have the potential to be more abundant in dry
ponderosa pine forest types because they occupy much smaller territories than woodpeckers.
However, nuthatches are weaker cavity-excavators and require more decay in their nesting
substrate in comparison to woodpeckers, and may also prefer different microhabitat structural
characteristics for nesting and foraging (Steeger and Hitchcock 1998).
A diversity of insectivorous bird species help to reduce insect populations (Bruns
1960, Holmes 1990, Torgersen et al. 1990, Machmer and Steeger 1995, Steeger and
Hitchcock 1998, Murakami and Nakano 2000), and lessen the impact of insect epidemics
(Korol 1985, Otvos 1979). Red-breasted and Pygmy Nuthatches reduce populations of adult
western (Dendroctonus brevicomis) and mountain (D. ponderosae) pine beetles by up to 26%
during outbreaks (Stallcup 1963, Otvos 1979). Red-breasted Nuthatches are also important
predators of Douglas-fir tussock moth (Orgyia pseudotsugata), as well as jack pine budworm
{Choristoneura pinus) and eastern spruce budworm (C. fumiferana\ Mattson et al. 1968,
Crawford et al. 1983). Leaf bugs (Pseudococcid spp.) are preyed upon by Pygmy Nuthatches
(Bent 1964, Stallcup 1963, Anderson 1976, Otvos and Stark 1985, and Campbell et al. 1988).
White-breasted nuthatches prey upon gypsy moths (Lymantria dispar) and tent caterpillars
(Malacosoma spp.). All three western nuthatches also prey upon weevils (Sitophilus spp.),
spruce budworm (Choristoneura spp.), wood-boring beetles (Cerambycidae spp. and
Buprestidae spp.; Bent 1964, Stallcup 1963, Anderson 1976, and Campbell et al. 1988), and

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larch casebearer (Coleophora laricella\ Sloan and Coppel 1968). Nuthatches prey upon
insects that are more likely to be missed by other bark foragers; they are the only species that
forage while traveling down the trunk of the tree. Nuthatches forage upon trees that are
heavily used by woodpeckers, looking opportunistically for any larval bark beetle or other
insects that have been exposed by foraging woodpeckers (Kroll and Fleet 1979, Otvos 1979).
Although all three species of nuthatches found within western North America have
similar foraging techniques and selection of food items (Anderson 1976), they differ enough
in the placement of foraging effort on trees that they can all co-exist in the same forest
(Stallcup 1968). Red-breasted Nuthatches distribute their foraging effort evenly upon trees
(Stallcup 1968, Airola and Barrett 1985, Carey et al. 1991). Pygmy Nuthatches spend a large
proportion of their time foraging on the distal ends of branches among the buds and terminal
foliage at the tops of trees (Stallcup 1968, Bock 1969, Szaro and Baida 1979, Airola and
Barrett 1985, Stone et al. 1999). White-breasted Nuthatches forage most often on the bole
and proximal portions of branches in the middle and lower portions of trees (Stallcup 1968,
Bock 1969, Szaro and Baida 1979).
Trunk-foraging species such as nuthatches may play an important role in snag cycling
within ponderosa pine ecosystems (Farris et al. 2004). There was a positive correlation
between the amount of foraging by woodpeckers and the amount of decay in snags of
ponderosa pine within central Oregon (Farris et al. 2004). One reason for this is that
woodpeckers may pass decay fungi from tree to tree with their bills (Farris et al. 2004). Of
birds that had their beaks sampled for presence of wood-decaying fungi, all cavity-nesting
species tested positive. Hairy (Picoides villosus), White-headed (P. albolarvatus), and
Black-backed (P. arcticus) Woodpeckers had detection frequencies ranging from 0.50 to

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0.57. Red-breasted Nuthatches had a detection frequency of 0.80 (Farris et al. 2004).
Although this has not been investigated, nuthatches may also serve as vectors for
transmission of these fungi.
In addition to supplying tree cavities and decreasing population sizes of forest insect
pests, nuthatches may provide important cues for migrant birds returning from wintering
grounds, according to the heterospecific attraction hypothesis (Monkkonen et al. 1997).
When resident birds were experimentally eliminated from islands in northeastern Minnesota,
some migrant populations were less abundant. Also, some migrant birds were more
abundant on islands where resident bird populations had been increased, when compared to
islands where resident bird populations had not been manipulated (Monkkonen et al. 1997).
1.3. Previous Research on the Effects of Restoration Treatments on Cavity-nesting
Birds
1.3.1. Silvicultural Thinning
The effects of forest thinning on cavity-excavating birds are most dramatic when the
treatment reduces the number of snags available for excavation. If nest-site availability is a
limiting factor within a forest, a reduction in snag numbers may cause a decreased density of
cavity-nesters the following season, regardless of other effects of the treatment (Chambers et
al. 1999). White-breasted Nuthatches may be more resilient than other cavity nesters to a
decrease in snag density because of their tendency to use natural cavities (McPeek et al.
1987, Brawn and Baida 1988b, Waters et al. 1990, Pravosudov and Grubb 1993, Bock and
Fleck 1995). However, thinning stands increases the vigor of remaining trees, reducing decay
in live stems and so reducing the creation of some types of natural cavities (Filip et al. 1995).
As a result of these effects, birds may use nest trees with less desirable microhabitat
characteristics, because they will have few choices for nest-sites within their territories
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(Tobalske 1992). An alteration of nest-site microhabitat can affect the nest microclimate,
predation rates, and nestling provisioning (Easton and Martin 2002). One simple way to
counteract this management effect is to add nest boxes to treated areas. The addition of nest
boxes in ponderosa pine forests of Colorado and northern Arizona increased densities of
Pygmy, Red-breasted, and White-breasted Nuthatches (Brawn 1987, Bock and Fleck 1995).
The effects of thinning on foraging behavior of bark-gleaning birds are difficult to
quantify. Birds can vary their foraging behavior and prey selection among years (Szaro et al.
1990), months (Hejl and Vemer 1990), stages of the breeding cycle (Sakai and Noon 1990,
Kelly and Wood 1996, Dobbs and Martin 1998), and even with time of day (Kleintjes and
Dahlsten 1995, Kelly and Wood 1996). There can also be a difference in the foraging
behavior based on sex (Grubb and Woodrey 1990, Hanowski and Niemi 1990, Kleintjes and
Dahlsten 1995, Sodhi and Paszkowski 1995, Kelly and Wood 1996), age, and dominance
status (Grubb and Woodrey 1990) of birds.
Avian population monitoring is often used as a tool to infer the quality of foraging
habitat. However, studies have shown that all foraging and nesting guilds can have mixed
responses to forest management (Saab and Powell 2005). Bark-foraging birds were detected
more frequently within thinned than unthinned forests of Washington (Artman 2002) and the
Oregon Coast Range (Hagar et al. 1996). Cavity-nesting birds were detected more frequently
in thinned units than ‘control’ units in the Sierra Nevada range of California (Siegel and
DeSante 2003). In Brazil, Aleixo (1999) reported that bark gleaners preferred to forage
within intact forest rather than selectively logged forest. Pygmy Nuthatches were less
abundant in partially logged than unlogged forests of ponderosa pine (Hejl 1994). Red­
breasted Nuthatches, along with all other cavity-nesters studied, declined in thinned areas on

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Vancouver Island, British Columbia (Beese and Bryant 1999). Red-breasted Nuthatches
showed no preference between ‘control’ units and units with various degrees of silvicultural
thinning in Douglas-fir forests of Oregon (Hagar 1999) or ponderosa pine forests in
northeastern Wyoming (Anderson and Crompton 2002). Although the response of birds
appears mixed, the responses tended to be stronger with increasing severity of thinning
disturbance in the studies that tested for this effect (Beese and Bryant 1999, Chambers et al.
1999).
There is often a correlation between population density of nuthatches and vegetation
characteristics that may be affected by thinning. The density of White-breasted Nuthatches
was negatively correlated with foliage volume in eastern hemlock (Tsuga canadensis;
Tingley et al. 2002) and oak/hickory (Carya spp.) forests (Showalter and Whitmore 2002).
White-breasted Nuthatches tend to prefer nest sites with a greater percentage of canopy
closure than found on average (Beier et al.2000). Canopy cover affected the abundance of
Red-breasted Nuthatches within Idaho, with a greater abundance of birds within stands with
greater canopy closure (Medin 1985). Alternatively, Pygmy Nuthatches were found only in
forests with less than 70% canopy closure (Baida et al. 1983, Csuti et al. 1997, Kingery and
Ghalambor 2001). Brown-headed Nuthatches (Sittapusilla, a morphologically similar
species to Pygmy Nuthatch) were negatively affected by increasing canopy cover in forests
composed of Loblolly pine (Pinus taeda) in Florida (Lohr et al. 2002).
Source and sink dynamics, especially in the case of an attractive sink, make it
difficult to conclude that there is no difference in habitat quality between two sites that
exhibit the same densities of birds (Delibes et al. 2001). Sources and sinks can be
differentiated by measuring fecundity. Attractive sinks are habitats which are superficially

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attractive to birds, but which provide poor nesting or foraging resources. Birds in source
habitats usually have higher fecundity than birds in sink habitats. The entire group of cavitynesting birds present within Sierran mixed conifer stands had significantly more nests, and
more successful nests, in thinned than unthinned units (Siegel and DeSante 2003).
Examining the number of young fledged from nests uses a finer scale than simply
quantifying successful versus unsuccessful nesting attempts. Red-naped Sapsuckers
(Sphyrapicus nuchalis) did not fledge a significantly different number of young from nests in
thinned or control units (Tobalske 1992).
1.3.2. Understory Burning

The effects of habitat burning on birds have been extensively documented. In one of
the earliest reports, Edwards and Ellis (1969) recorded the arrival of Mourning Doves
(Zenaida macroura), quail (Callipepla spp.), and an American Woodcock (Scolopax minor)
to the site of a grassland fire while it was still burning. A review of the literature shows
mixed effects of burning on birds within all foraging and nesting guilds; however, most
studies reported either positive response or no response of cavity-nesters and barkinsectivores to stand-replacing bums (Saab and Powell 2005). Cavity-nesting birds tend to
increase in abundance after prescribed fire (Bunnell 1995, King et al. 1998, Dieni and
Anderson 1999, White et al. 1999); however, research suggests that the response is limited to
the year after the bum (Bock and Bock 1983, Dieni and Anderson 1999, Huff and Smith
2000). Cavity-nesting species generally increase as snag density increases, and most burning
treatments create snags (Showalter and Whitmore 2002). However, the amount of decay
needed to allow the excavation of a nest depends upon the strength of the excavator, but
generally snags accumulate cavities as they decay (Swallow et al. 1986). It took 25 years for

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most ponderosa pine and Douglas-fir to reach decay classes that were most frequently
excavated, and most cavity-bearing snags were found on bums over 20 years old (Lehmkuhl
et al. 2003). The response of birds to prescribed burning tends to intensify with increasing
bum area (Dieni and Anderson 1999).
1.3.3. Restorative Treatments
No published studies have documented the effects of restorative treatments on
western North American nuthatches. Restorative treatments in pine have increased the
abundance of Brown-headed Nuthatches in southeastern North America (Conner et al. 2002),
and increased the fecundity of Western Bluebirds (Sialia mexicana; Germaine and Germaine
2002). When studied as a group, however, birds tend to respond in a species-specific way to
thinning and burning treatments that are applied in a restorative context. Hannon (2000)
found that no foraging or nesting guild responded to restorative treatments consistently.
Instead, one species was more abundant in burned stands, two species were more abundant in
thinned stands, two species were more abundant in both treatments, and four species were
found in the same abundance in treated and control stands. Birds within ponderosa pine
forests may not respond to restoration consistently across foraging or nesting guilds.
Because restoration treatments are needed on a landscape scale within ponderosa pine forests
of western North America, it is important to investigate the effects of treatments on avian
species.
Few studies have focused on the habitat requirements of species in the nuthatch
family in western North America (but see Sydeman 1989, Adams and Morrison 1993,
Steeger and Hitchcock 1998). Even fewer studies have documented restorative-type
disturbance on nuthatches (but see Wilson and Watts 1999). Research needs to be conducted

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to determine how restorative treatments affect nuthatches, before such treatments are widely
used by land managers (Block et al. 2001).
1.4. Hungry Bob Study Site and Restorative Treatments
1.4.1. Hungry Bob
The ‘Hungry Bob’ research units were located within the Wallowa-Whitman National
Forest in the Blue Mountains of northeastern Oregon (45° 37’ N, 117° 15’ W; Fig. 1.5).
Ponderosa pine and interior Douglas-fir predominated, with western larch (Larix
occidentalis) and lodgepole pine (Pinus contorta) found less commonly. Grand fir (Abies
grandis), and western juniper (Juniperus occidentalis) were rarely present. The understory
of the area was typically dominated by snowberry {Symphoricarpos albus) and pine grass
(Calamagrostis rubescens). Study units were located mostly on ridge tops above steep
valleys, with a range in elevation of 1113 to 1388 m.
The history of the site included fire suppression over the last century, selective
harvesting from 1910 to 1996, and prescribed burning in some areas over the last 20 years (J.
Mclver, Forester, USDA Forest Service, pers. comm. 2003). The Blue Mountains of
northeastern Oregon historically received ground fires on an average interval of 10 years, but
the actual frequency ranged from 3 to 30 years (Agee 1993). These low-severity fires burned
400,000 acres or more in an average year until the 100% fire suppression initiative in 1906
(Hall 1980, Wickman 1992, Agee and Maruoka 1994, Bailey and Covington 2002). Forests
in the Blue Mountains were experiencing extensive insect infestation, more frequent highseverity fires, and increased incidence of disease as a result of the change in the natural fire
regime in the area, combined with other forest management decisions (Filip et al. 1996,

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- -

: Ponderosa Pine Ecosystems

?=vv^-j '

Wallowa-Whitman National Forest

S

M l RFKIW

O im m

uiwm

Ii(>r

■smmcm

# » —w *

t
4
#/

j
USDA Forest Service

Figure 1.5: Hungry Bob location within northeastern Oregon (United States Geological
Survey and United States Department of Agriculture Forest Service).

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Jaindl et al. 1996). Dwarf mistletoes (Arceuthobium douglasii, A. laricis, A. campylopodum,
and A. americanum), indian paint fungus (Echinodontium tinctorium), Douglas-fir tussock
moth, larch casebearer, western and mountain pine beetle, and Douglas-fir beetle
(Dendroctonus pseudotsugae) were among the forest health problems present in the Hungry
Bob study area (Filip et al. 1996).
1.4.2. Restorative Treatments
The research units and treatments were established by scientists from the Pacific
Northwest Research Station and Oregon State University. This interdisciplinary research
project was funded by the United States government through both the Fire/Fire Surrogate
Study and the Wallowa-Whitman National Forest Service. The study units were designed to
include four treatments (prescribed burning only -‘bum’, mechanical thinning only -‘thin’,
mechanical thinning followed by prescribed burning -‘thin and bum’, and no treatment ‘control’) with four replicates of each treatment. Thus, a total of 16 experimental units were
established in December of 1997. The treatment units ranged in size from 6.8 to 32 ha, with
an average size of 17 ha. Study units of this size are large enough for several pairs of
nuthatches to occupy, and also small enough to have replicates within the same forest type
(Enoksson and Nilsson 1983, Brown 1985, Chambers et al. 1999). The treatment units were
designed with an irregular shape because of patchy forestation and also to avoid areas that
had recently (within the last 20 years) been thinned or burned. Reference markers were set in
a grid with permanent rebar (‘bum’ and ‘thin and bum’) or wooden stakes (‘thin’ and
‘control’) 50 m apart to aid in orientation within the stands while collecting data.
Mechanical thinning on the ‘thin’ and ‘thin and bum’ study units was performed in
the summer and fall of 1998 with the use of a single-grip harvester and forwarders. Slash

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was left on the sites, but the trees were removed and sold to recuperate the expense of the
treatment (J. Mclver, Forester, USDA Forest Service, pers. comm. 2003). Prescribed
burning on the ‘bum ’ and ‘thin/bum’ units was accomplished in the fall of 2000. Large
woody debris was removed from around veteran ponderosa pines, but the forest floor was not
raked away from the base of the trees (J. Mclver, Forester, USDA Forest Service, pers.
comm. 2003). Standing dead trees were intentionally left on all treatment units. The
restorative treatments were performed with the desire to protect 80% of the stand from a
wildfire that may occur under weather conditions that would normally produce unacceptable
risk of a crown fire (within the 80th percentile, determined by an average of 15 years of data
at the closest fire weather station; Weatherspoon 2000). To achieve this goal, a desired
future condition (DFC) was established for all treated stands. The DFC was set to require a
basal area of trees close to 16 m /ha, while retaining dominant and co-dominant crown
classes (especially trees greater than 53 cm dbh) and also creating an irregular spacing of
individual trees to simulate natural distribution (Weatherspoon 2000). To attain a stand
structure that most closely approximated that found within mature ponderosa pine stands,
large (>50 cm dbh) old (>150 years) dominant trees were protected by removing all
competing conifers within a 9 m radius (Weatherspoon 2000).
1.5. Thesis Objectives: Determining the Effects of Restorative Treatments on
Nuthatches
Cavity-nesting and bark-foraging birds are sensitive to landscape-level changes in
forest structure (Dickson et al. 1983, Angelstam and Mikusinski 1994). This thesis aims to
determine whether cavity-nesting and bark-foraging birds may be sensitive to changes in
forest structure on a smaller scale. Occupancy of an area has been linked to fecundity and
food availability and thus to habitat quality for avifauna (Enoksson and Nilsson 1983, Sergio

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and Newton 2003). For this reason, many studies concerned with documenting the effects of
forest management practices on avian species have focused on species abundance, as
measured by distance-sampling or encounter rates (Bock and Lynch 1970, Beese and Bryant
1999, Artman et al. 2001, Gram et al. 2003). Within this thesis, the number of birds
encountered per observation period was compared among treatments.
The density of territories within an area has been linked to fecundity and food
availability and thus to habitat quality for avifauna (Enoksson and Nilsson 1983, Sergio and
Newton 2003). Within this thesis, the number of nuthatch nests within each treatment and
each year unit was compared among treatment types. While measurements of abundance do
address the ability of the habitat to provide the birds with the basics of survival, they fail to
address the finer details of habitat quality that may affect nesting success and foraging
patterns. One of the areas that requires further research is the effect of fire upon nesting
success (Saab and Powell 2005). Modeling daily nest survival using methods that allow nest
success to vary over time have been underutilized but may be much more effective than
traditional methods (Dinsmore et al. 2002). Daily survival of nests of Red-breasted
Nuthatches was analyzed within this thesis using an information theoretic approach.
Research that leads to better understanding the underlying causes of abundance and
nest-survival differences among different habitats is also needed (Saab and Powell 2005).
Quantifying and comparing foraging patterns among species and among treatment units can
reveal differences in niche partitioning as well as functional responses of foraging birds
among habitats with different attributes. The rate of travel for foraging birds has been shown
to be inversely proportional to resource abundance, including food and cover (Morrison et al.
1987). In Lesser Spotted Woodpeckers (Dendrocopos minor), a positive correlation between

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length of time of substrate use and food availability was reported (Olsson et al. 2001). In this
thesis, the amount of time that nuthatches stayed on individual trees while foraging was
compared among treatments. The number of seconds nuthatches spent foraging upon trees
was compared to the structural characteristics of the trees within this thesis.
Foraging effort was positively correlated to predation risk in Eurasian Blackbirds
(Turdus merula; Post and Gotmark 2006). Therefore, a difference in the proportion of time
spent foraging among treatments might indicate foraging success differences among
treatments. This was compared among species and treatments for nuthatches within this
thesis. A difference in the use of foraging zones depending upon the treatment type would
indicate a difference in prey abundance or quality within different areas of the trees and an
adaptation by the nuthatches to this variation in food resources (Block 1990).
In summary, the objectives of this study were to: 1) determine whether restorative
treatments in ponderosa pine influence the density of foraging Pygmy, White-breasted, or
Red-breasted Nuthatches; 2) determine whether restorative treatments in ponderosa pine
influence the foraging behavior of nuthatches; 3) describe the structural characteristics of
trees used for foraging by nuthatches; 4) determine whether restorative treatments in
ponderosa pine influence the density or daily survival of nests of nuthatches; 5) report on the
nest-site characteristics of nuthatches within northeastern Oregon. This information was
used to determine which restorative treatments, if any, were most beneficial for nuthatches
within ponderosa pine forests of northeastern Oregon. It will also add to the general
knowledge base of life history characteristics of western North American nuthatch species.

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2. The effects of restorative treatments in ponderosa pine (Pinusponderosa) on the
foraging ecology of nuthatches (Sitta spp.) in northeastern Oregon
2.1. Abstract
Fire exclusion and other forest management practices have shifted the fire regime o f
ponderosa pine (Tinus ponderosa,) ecosystems from frequent understory fires to infrequent,
crowning wildfires to which the organisms associated with them have not adapted.
Mechanical thinning and prescribed burning are the most common methods o f restoring
forests to their historic conditions; however, their effects on biological aspects o f ecosystem
function, such as avian foraging dynamics, are poorly understood. These effects need to be
researched as part o f a careful evaluation o f different restorative treatments before they are
widely used. Restorative treatments ( ‘thin’, ‘burn’, ‘thin and burn’, and ‘control’) were
applied to ponderosa pine forests within northeastern Oregon. The foraging behavior o f
White-breasted fSitta carolinensisj, Red-breasted (S. canadensis,), and Pygmy (S. pygmaea,)
Nuthatches was determined using the focal animal sampling technique. White-breasted and
Pygmy Nuthatches were encountered most frequently within ‘thin and burn ’ treatment units.
This abundance difference among treatments did not appear to be due entirely to
characteristics o f the trees found in each treatment. Red-breasted Nuthatches altered the
amount o f time spent on individual trees among treatment types, but not among trees with
different structural attributes. Structure differed between trees used fo r foraging and those
not used fo r each species o f nuthatch. The birds did not alter their use o f zones o f the trees or
the amount o f time they spent in non-foraging behavior among treatments. The results
suggest that thinning alone may be less beneficial to nuthatches than burning alone or
thinning combined with burning. Further research on foraging behavior that incorporates
greater complexity may better explain the variations in foraging patterns found in this study.

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2.2. Introduction
A century of fire suppression initiatives within western North America have
contributed to the loss of ponderosa pine ecosystems (Allen et al. 2002, Brown et al. 2004).
Increased fire-retum intervals within these forests have allowed greater tree recruitment and
retention, have increased the proportion of shade-tolerant species such as Douglas-fir
(Pseudotsuga menziesii) and true firs (Abies spp.), and have also increased fire-fuels (Swezy
and Agee 1991, Covington and Moore 1992, Mutch et al. 1993, Agee and Maruoka 1994,
Harrod et al. 1998). These changes in forest composition and structure have contributed to
an increase in crowning wildfires within ponderosa pine (Agee 1996). Between 1991 and
2001, approximately 500,000 acres of ponderosa pine within northeastern Oregon was
destroyed by wildfire (J. Mclver, Forest Ecologist, USGS, pers., comm., 2003). An
estimated 3 million acres of forest within Oregon and Washington are in need of restoration
(Caraher et al. 1992). Mechanical thinning and prescribed burning are the most common
methods of restoring fire-suppressed forests to their historic conditions (Agee and Maruoka
1994, Hayes et al. 1997, Ottmar and Sandberg 2001), and have both been responsible for
decreasing fire intensity when they are applied to ponderosa pine forests (Pearson et al. 1972,
Pollet and Omi 2002). Cavity-nesting and bark-foraging birds are sensitive to landscapelevel changes in forest structure (Dickson et al. 1983, Angelstam and Mikusinski 1994);
therefore, the effects of restorative treatments on these birds need to be researched before
they are widely used by land managers (Block et al. 2001).
Three species of cavity-excavator present within the Blue Mountains of Oregon are
nuthatches (Sitta): White-breasted, Red-breasted, and Pygmy. Nuthatches, especially the
Pygmy Nuthatch, may have developed fire-dependent foraging techniques owing to their

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residence within ponderosa pine ecosystems, yet few studies have documented the effects of
restorative treatments on the foraging ecology of nuthatches.
The objectives of this study were as follows: 1) to determine whether nuthatches
were encountered more frequently among treatments as a measure of species use and as an
estimate of species abundance; 2) to determine whether the amount of time spent foraging on
each tree varied among treatments or with structural characteristics of the trees; 3) report on
the structural characteristics of trees foraged on by nuthatches within different restorative
treatments; and 4) to determine whether the proportion of time birds spent foraging as
opposed to other activities such as territory defense differed among treatments. General
foraging behavior was used as an indication of where food resources were most abundant,
detectable, and desirable within different treatments.
2.3. Methods
2.3.1. Study Site
The ‘Hungry Bob’ research units were located within the Wallowa-Whitman National
Forest in the Blue Mountains of northeastern Oregon (45° 37’ N, 117° 15’ W). For a detailed
description, please see section 1.4.
2.3.2. Treatments and Study Units
The study units were designed to include four treatments (prescribed burning only ‘bum ’, mechanical thinning only -‘thin’, mechanical thinning followed by prescribed burning
-‘thin and bum ’, and no treatment - ‘control’) with four replicates of each treatment. For a
detailed description, refer to section 1.4.

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2.3.3. Foraging Ecology
2.3.3.I. Foraging Behavior
Quantifying food abundance for generalist insectivores such as nuthatches requires a
wide range of arthropod sampling techniques, which are time-consuming and expensive
(Raphael and Maurer 1990, Wolda 1990). Quantification of food items taken by birds
through the use of stomach content analysis, forced regurgitation, flushing, or ligatures were
impractical for this study because of mortality, increased handling, and limited access to
nuthatch nests. Quantification of prey items by direct observation was not attempted because
of the subtle nature of gleaning attacks, which results in a bias towards large prey items
(Robinson and Holmes 1982, Rundle 1982, Rosenberg and Cooper 1990). Therefore,
observations of foraging behavior were performed using the focal animal technique (Martin
and Bateson 1986), and were modified from those used by Weikel and Hayes (1999). Adult
nuthatches were followed as they were encountered during a structured walk of each unit
between sunrise and 14:00 hrs (Weikel and Hayes 1999). Foraging data were collected for
two years between April 20th and July 30th, 2003 and 2004. During the observation periods,
a hand-held voice recorder was used to document the behavior of nuthatches, with a focus on
foraging behavior. The foraging observation period proceeded following these steps:
1)

The research unit was walked for two hours following the sequentially numbered plot
markers, alternating the sequence of plots on each visit.

2)

When a nuthatch was encountered, the observation period clock was paused, and the
bird was followed to the next tree to which it flew.

3)

The amount of time (in seconds) spent in each behavior (Table 2.1) while upon the
substrate as well as the bird’s position upon the substrate (Fig. 2.1.) was recorded.

4)

The tree was marked with a unique and removable tag.

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Table 2.1. Classification of the behaviors of nuthatches (based on Remsen and Robinson
1990).
Behavioral Class
Search for Food

Activity
glean
probe
peck
scale/flake

Detail of Activity
search for food traveling on the bole of the tree
insert the bill into a crack or crevice
force the bill beneath the surface of the substrate
peel off the surface of the substrate with the bill

Attack Food

capture
flycatch

capture a food item while upon tree surface
capture food while flying or diving in the air

Food Handling

handle prey

to rub, jab, probe, or grasp food to prepare it for
eating, or to take back to nestlings

Territory Defense

sing
fight/chase
display
call

series of calls while perching or foraging
chase another bird from the area
fluff feathers, flick wings, raise crest
single notes, irregularly delivered

Other

preen
excavate
mob
perch

clean feathers while perched
use bill to dig a nest cavity in soft wood
join conspecifics in the pursuit of a predator
sit in a stationary position, not actively gleaning

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Figure 2.1: Foraging zones within a typical ponderosa pine on the Hungry Bob
research units within northeastern Oregon.

27

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5)

Steps 3 and 4 were followed at each successive foraging substrate until the bird
disappeared from view.

6)

Once the bird was lost from view, the observer resumed the observation period clock
and resumed walking the unit along the plot line until another nuthatch was
encountered, or the observation period was over.

7)

Tree structural and microhabitat measurements were taken from each tree that was
foraged upon after the observation period.

8)

The removable tag was replaced with a permanent mark on the bark of each tree.
(K.L. Farris, Ecologist, WCS, pers. comm. 2002)
No units were surveyed under weather conditions that might have affected the

foraging patterns of birds, such as heavy rain, sleet, or snow. No units were surveyed under
conditions that might have affected an observer’s ability to follow a foraging individual, such
as fog or high winds. Observation periods were staggered throughout the day to avoid bias
due to daily foraging patterns, but ended no later than 14:00 hrs on any day (Adams and
Morrison 1993, Weikel and Hayes 1999). Recording sequential observations helped to avoid
biasing behavioral observations towards conspicuous or long-lasting behaviors (Morrison
1984, Noon and Block 1990). Nuthatches are generally tolerant to researchers in the field
(Brokaw 1893, Jones 1930). However, to ensure that behaviors recorded were minimally
influenced by observation, observers practiced watching nuthatches in the field prior to data
collection each year. When the researcher was too close, the bird would flush from the tree,
circle the bole of the tree, or freeze. No observer reported these behaviors by a foraging
nuthatch except in response to interactions between other birds or predators. All attempts
were made to keep track of the same foraging individual that was initially observed. If an
individual was ‘lost’ at any point during the observation period, the observer would track a

28

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minimum of 100 m from the site before recording additional behavior data to avoid
pseudoreplication.

2.3.3.2. Structural Characteristics of Trees Used for Foraging
Once the observation period ended, structural data were collected from each tree that
had been foraged upon. Variables recorded were: (1) diameter at breast height; (2) height
category of the tree (Table 2.2); (3) % of crown connected to the canopy; (4) % of the height
of the bole with live branches; (5) species of tree; and (6) average depth of the furrows in the
bark. The depth of bark furrows was estimated as described by Weikel and Hayes (1999).
Four measurements were recorded of the deepest furrow of the bark within each quadrant of
the bole of the tree, and then averaged. Structural measurements were also taken from an
equal number of trees that were not foraged upon during any foraging observation, as
determined by the permanent markers placed upon the bark of foraged trees.
2.3.4. Analysis
2.3.4.I. Use of Treatment Units by Birds
To determine whether nuthatches were encountered at different rates within different
treatment types, the number of nuthatches observed foraging within each treatment unit
during each observation period was compared using a Kruskal-Wallis test. ANOVAs were
not used for these comparisons because the data were non-normal. Data consisted of many
0’s, especially for Pygmy and White-breasted Nuthatches. This should not deter the use of a
Kruskal-Wallis test (Conver 1999). Analyses were separated by bird species, resulting in
three tests. Tests were run in MINITAB (Version 14, 2003; Tabachnick and Fidell 2000).
Post-hoc multiple comparisons were done using the methods described in Siegel and

29

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Table 2.2. Height categories recorded from each tree foraged upon by nuthatches.
Height Category
1
2
3
4
5

Height of Tree (m)
<11
11-15
16-20
21-25
>26

30

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Castellan (1988). The alpha level for each test was set at 0.05.
2.3.4.2. Differing Use of Trees Among Treatment Types
The number of seconds that birds foraged upon each tree was compared among
treatments using a Kruskal-Wallis non-parametric test. Behavioral data consisted of 23
observations of Pygmy Nuthatches, 109 observations of Red-breasted Nuthatches, and 64
observations of White-breasted Nuthatches. Each observation was the average number of
seconds that a nuthatch was observed foraging upon each tree. Up to eight trees were
recorded per observation of a nuthatch. Only trees with complete observations were
considered. A complete observation occurred when the observer was able to see the bird
land on the tree and was able to collect behavioral data from the bird until it flew from the
tree. Because of limited samples, data were pooled between years and treatment units, but
separated by bird species. Due to unequal sample sizes and non-normal data, ANOVA was
not used for this analysis.
Structural characteristics of trees used for foraging by Red-breasted and White­
breasted Nuthatches were compared with the number of seconds that birds foraged upon
them using mixed linear models. Models could not be fitted for Pygmy Nuthatches due to
small sample sizes. Fixed factors within the models included: tree species, treatment, and
height categories. Bird I.D. was used as a random factor because up to eight trees foraged by
the same bird were included in the analysis. Red-breasted Nuthatches are generalist foragers
(Stallcup 1968), so models were designed to compare bole characteristics, crown
characteristics, and a combination of bole and crown measurements. White-breasted
Nuthatches are trunk foragers (Stallcup 1968), so models were designed to compare different
aspects of tree size as well as the proportion of the bole that was not covered by live crown.

31

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Candidate models were compared using Akaike’s Information Criterion adapted for small
sample sizes (AICc, Hurvich and Tsai 1989; Tables 2.3 and 2.4; Burnham and Anderson
2002). This was undertaken to determine whether structural characteristics or treatment type
influenced the amount of time birds stayed on individual trees (Adams and Morrison 1993).
Only trees with complete observations were included in the analysis.
Structural characteristics of trees that were foraged upon by nuthatches were
compared with the structure of non-foraged trees with binomial logistic regressions using an
information theoretic approach (Rodewald and Smith 1998, Steeger and Hitchcock 1998,
Weikel and Hayes 1999, Anderson and Crompton 2002). Candidate models were developed
based on what the literature has shown affects the use of trees by nuthatches for foraging
(Table 2.5). For example, Pygmy Nuthatches often forage within the canopy (Stallcup 1968),
so models were designed to compare tree size as well as canopy characteristics. Candidate
models were compared using Akaike’s Information Criterion adapted for small sample sizes
(AICc, Hurvich and Tsai 1989, Burnham and Anderson 2002). Predictive ability of the
models were assessed using receiver operating characteristic (ROC) scores (Zweig and
Campbell 1993). Models with ROC scores exceeding 0.70 were considered useful models
(Swets 1988, Manel et al. 2001). In order to avoid correlation between variables included
within each model, Principle Components Analysis (PCA) was used (Lawley and Maxwell
1962). Three PC As were used for each species of Nuthatch. One was used to combine
diameter, height, and depth of furrows. This component ,’tree size’, accounted 76.70% of the
variation in the data for Red-breasted Nuthatches, 77.46% for Pygmy Nuthatches, and
82.10% for White-breasted Nuthatches. One PCA was used to combine diameter and furrow

32

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Table 2.3. Candidate models to predict the number of seconds that Red-breasted
Nuthatches foraged upon each tree using treatment and tree structure.
Variable
Treatment
Height
Diameter
Furrow Depth
Canopy Connections
Crown Ratio

Model

1

2
X
X
X
X
X
X

3

4
X

5
X

X
X
X
X
X

X
X

7
X
X

6

8

10

X
X
X
X

X
X
X
X

X

X
X
X
X

9
X

X
X

Table 2.4. Candidate models to predict the number of seconds that White-breasted
Nuthatches foraged upon each tree using treatment and tree structure.
Variable
Treatment
Height
Diameter
Furrow Depth
Crown Ratio

Model

1

2
X
X
X
X
X

3

4
X

X
X
X
X

5
X
X
X

6

7
X
X

X

X

X

8

X
X

33

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Table 2.5. Candidate models to predict the structural characteristics of trees that
nuthatches foraged upon.
Variable
Tree Size
Tree Species
Height
Height +
Diameter
Diameter
Diameter +
Furrow
Canopy
Connections
Crown Ratio

Model

1

2
X

3
X
X

4

5

6

X

X

8

9

X

X
X

X

X
X

7

10

11
X

X

X

12
X
X

13
X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

34

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depth. This component, ‘diameter/furrow depth’, accounted for 86.19% of the variation in
the data for Red-breasted Nuthatches, 90.25% for Pygmy Nuthatches, and 89.17% for White­
breasted Nuthatches. The last PCA was used to combine diameter and tree height. The
resulting component, ‘diameter/height’ accounted for 85.81% of the variation in the data for
Red-breasted Nuthatches, 82.93% for Pygmy Nuthatches, and 88.40% for White-breasted
Nuthatches. The broken-stick method was used to evaluate the components produced by
PCA (Frontier 1976, Jackson 1993). All variables were positively correlated with the
components. Larger values of diameter, height, and furrow depth resulted in larger values of
‘tree size’, ‘diameter/furrow depth’, and diameter/height’.
Analyses were run using SPSS (Version 14, 2005) and MINITAB (Version 14, 2003).
Post-hoc multiple comparisons for Kruskal-Wallis tests were performed using methods
described in Siegel and Castellan (1988). The alpha level for each test was set at 0.05. Cases
with standardized residuals >2.58 or <-2.58 and Cook’s distance of < 1 were eliminated as
outliers within analyses.

2.3.4.3. Structural Differences Among Trees Within Each Treatment Unit
Structural characteristics of trees within each treatment unit were compared using
data collected by the Pacific Northwest Research Station in LaGrande, OR and donated by
Andy Youngblood (Research Forester). Diameter, height, crown ratio, canopy connections,
furrow depth, and tree species composition were compared using Kruskal-Wallis H tests
(SPSS Version 14, 2005). Multiple comparisons after Kruskal-Wallis were performed
according to Siegel and Castellan (1988).

35

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2.3.4.4. Behavior Differences Among Treatment Units
The proportion of observation time that each bird was documented in non-foraging
behavior (singing, preening, perching, calling, aggressive territorial encounters, displaying,
or excavating a cavity) was compared using a Kruskal-Wallis non-parametric test
(Tabachnick and Fidell 2000). A nonparametric test was used because these data were not
normally distributed, and sample sizes were unequal among treatment types. These analyses
were undertaken to determine whether nuthatches differed in the proportion of time that they
spent foraging among treatment types.
The number of seconds each bird was observed within each foraging zone (Fig. 2.1)
was converted to the proportion of time each bird spent within each zone (Stallcup 1968).
Transforming the data into continuous proportional data tended to create Is and Os. All Is
and all Os within the data were converted in the following manner (Zar 1999): If x =1 then x
was converted to 1-1/(4*seconds); If x=0 then x was converted to 1/(4*seconds). This
method allowed the 0 value to approach 0 and the 1 value to approach 1 as the bird was
watched a greater amount of time. At 400 seconds, the difference to 4 decimal places was
0.0006. At 10 seconds, the difference increased to 0.025. This reflected the fact that more
zones were foraged depending upon how long the bird was watched in each tree.
Comparisons were made among foraging zones along the horizontal and vertical axis (see
Table 2.6). Zones 3, 7, and 11 were used as buffer areas between proximal and distal branch
zones. For Pygmy Nuthatches, there were too few observations in ‘thin’ and ‘bum ’
treatments to allow comparison. Only observations lasting longer than 10 seconds were used
for the analysis (Morrison et al. 1987).

36

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Table 2.6. Zone combinations used to compare foraging of nuthatches along horizontal
and vertical axes.
Zones Combined
1,5,9
2,6,10
4,8,12
1,2,3,4
5,6,7,8
9,10,11,12

Variable
bole zones
proximal zones
distal zones
top zones
middle zones
bottom zones

Axis of Comparison
horizontal
horizontal
horizontal
vertical
vertical
vertical

57

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Analyses were run using SPSS (Version 14, 2005 and MINITAB (Version 14, 2003;
Tabachnick and Fidell 2000). Post-hoc multiple comparisons for Kruskal-Wallis tests were
done using methods described in Siegel and Castellan (1988). The alpha level for each test
was set at 0.05. Cases with standardized residuals >2.58 or <-2.58 and Cook’s distance of < 1
were eliminated as outliers within analyses.

2.4. Results
All treatments were given equal observation time while searching for foraging
nuthatches. For the purposes of analysis, all treatment units were pooled by treatment type.
Due to differences in encounter rates between species and treatments, Pygmy Nuthatches
were observed for a total of 123 minutes, Red-breasted Nuthatches were observed for 566
minutes, and White-breasted Nuthatches were observed for 416 minutes over the course of
two breeding seasons (See Table 2.7). The behavioral data that resulted were used to analyze
the similarity of foraging behavior and foraging location within trees between treatments.
All foraging observations of Pygmy Nuthatches and White-breasted Nuthatches in the
‘control’ treatment came from a single unit. One family group of cooperative nesters (4-5
birds) were the only Pygmy Nuthatches observed in this unit in both years of the study.
More individuals of White-breasted Nuthatch were seen foraging within the ‘control’ unit
than Pygmy Nuthatch. However, readers should interpret results obtained for Pygmy and
White-breasted Nuthatches within this ‘control’ unit with caution.
2.4.1. Use of Treatment Units by Birds
The number of foraging birds encountered during each observation period was
significantly different among treatments for both Pygmy Nuthatches (Kruskal-Wallis,

38

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Table 2.7. Amount of time (minutes) birds were observed foraging within each
treatment type. PYNU=Pygmy Nuthatch, RBNU=Red-breasted Nuthatch, and
WBNU= White-breasted Nuthatch.
Bird Species

PYNU
RBNU
WBNU
Total

______________________ Treatment_______________
Control
Thin
Bum
Thin and
Total
Bum
32
1
12
123
79
566
160
99
151
158
40
416
68
90
218
1106
230
168
253
455

39

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N=T10, 77=21.45,p<0.001; Fig. 2.2) and White-breasted Nuthatches (Kruskal-Wallis,
N=110; 77=10.43, p=0.015; Fig. 2.2). Post-hoc paired comparisons showed that Pygmy
Nuthatches were observed significantly more often within ‘thin and bum ’ treatments than
within either ‘thin’ treatments or ‘burn’ treatments (p<0.05). White-breasted Nuthatches
were encountered significantly more frequently in ‘thin and bum’ units than ‘control’ units
(p<0.05). The number of foraging birds observed was not significantly different between
treatments for Red-breasted Nuthatches (Kruskal-Wallis, N=110; H=5J7, p=0.123; Fig. 2.2).
Results of the Kruskal-Wallis test comparing encounters of Pygmy Nuthatches within
treatments must be interpreted with caution, as variances were not equal between groups for
this species. Unequal variances tend to inflate Type I error rates in Kruskal-Wallis tests
(Cribbie 2003).

2.4.2. Differing Use of Trees between Treatment Units
Red-breasted Nuthatches spent a significantly different amount of time upon trees
between treatment types (ICmskal-Wallis, N=109, 77=23.233,/?<0.001; see Fig. 2.3).
Multiple comparisons revealed that the birds spent less time on trees within ‘control’
treatments and ‘thin’ treatments than within ‘thin and bum’ or ‘bum’ treatments (p<0.05).
The test was not significant for Pygmy Nuthatches (Mann-Whitney, N=23, [7=41.0,/?<0.341;
see Fig. 2.3) or White-breasted Nuthatches (Kruskal-Wallis, N=64, 77=3.537, p<0.316; see
Fig. 2.3). A Mann-Whitney U test was used to compare data for Pygmy Nuthatches because
sample size did not permit the analysis of trees within ‘thin’ or ‘bum’ treatments.
The amount of time that Red-breasted Nuthatches foraged upon trees was best
predicted by a model that included only treatment type (Table 2.8). Treatment type was
significant within the model at an alpha level <0.001 (Table 2.9; Fig 2.4). ‘Thin and bum’

40

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TV
3
ua
9
O
u
S
w
*0
•P*
CO
o
u
X
S
9
£

70
Control

60
50
40
30
20
10
0
PYNU

RBNU

WBNU

Nuthatch Species
Figure 2.2: Number of nuthatches encountered within each treatment type.
PYNU=Pygmy Nuthatch, RBNU=Red-breasted Nuthatch, and WBNU=White-breasted
Nuthatch.

41

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120

Treatment

"

0

□ in

J§ 100

"

1
m
%
&
1

Control

1 3 Bum

i

so-

Tim and Bum

1

so-

‘S

i

% 40"

a

1

di
30"
$

—

r——

"— r—

BJBNTJ

PYNU

WBNU

Nuthatch Species
Figure 2.3: Mean rank of time (in seconds) each nuthatch species spent foraging upon
each tree within each treatment type. PYNU=Pygmy Nuthatch, RBNU=Red-breasted
Nuthatch, and WBNU=White-breasted Nuthatch. Lines represent medians, boxes
represent the interquartile range of the data, and error bars represent ± 1 Standard
Deviation.

42

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Table 2.8. Comparison of models using the structural characteristics of trees to predict
the length of time Red-breasted Nuthatches foraged upon them.
Model Parameters Included
4
7
5
6
9
2
1
8
10
3

611.967
615.272
622.612
636.902
625.282

A AICc Akaike
Weight
0.000 0.835
3.305 0.160
10.645 0.004
12.935 0.000
13.315 0.001

627.702

15.735

0.000

633.903
634.749
639.931
640.739

21.936
22.782
27.964
28.772

0.000
0.000
0.000
0.000

AICc

treatment
canopy connections + crown ratio + height + treatment
furrow + dbh + treatment
furrow + dbh
canopy connections + crown ratio + dbh + furrow depth
+ treatment
(global) treatment + height + dbh + furrow depth +
canopy connections + crown ratio
null
canopy connections + crown ratio + height
canopy connections + crown ratio + dbh + furrow depth
height + dbh + furrow depth + canopy connections +
crown ratio

Table 2.9. Parameter estimates (PE), standard error (SE), F -\alue, f-value, and p-value
of each variable within the best performing model using the structural characteristics of
trees to predict the length of time Red-breasted Nuthatches foraged upon them.
Variable
Intercept
Treatment
‘Control’
‘Thin’
‘Bum’
‘Thin and Bum’

PE
4.172

SE
0.151

-0.751
-1.135
-0.350
contrast

0.198
0.223
0.213

F
236.909
10.096

t
27.586
-3.802
-5.095
-1.646

43

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p-value
<0.001
<0.001
<0.001
<0.001
0.101

----------------- 1------------------------ 1------------------------ 1------------------------ J---------

Control

Thin

Bum

Him and Bum

Treatment

Figure 2.4: Mean amount of time (natural log of seconds) that Red-breasted
Nuthatches were predicted to forage upon trees within each treatment.

44

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was used as a contrast variable against which the rest of the treatments were compared.
Parameter estimates shown in Table 2.8 are negative for ‘control’, ‘thin’, and ‘bum’,
indicating that Red-breasted Nuthatches foraged upon trees in these treatments for a shorter
amount of time than in ‘thin and bum’ treatment units.
The model best predicted the amount of time that White-breasted Nuthatches foraged
upon trees included treatment type, which was not significant within the model at an alpha
level <0.05 (Table 2.10 and Table 2.11).
Tree species preference could not be analyzed with logistic regression for Pygmy
Nuthatches because the birds were recorded only twice upon Douglas-fir. The model that
included diameter and crown ratio best predicted which trees Pygmy Nuthatches used for
foraging (logistic regression, x = 42.169, N=155, p<0.001; Table 2.12). The bestperforming model had good predictive accuracy (ROC = 0.782). Pygmy Nuthatches foraged
upon trees with a larger diameter than average (Table 2.13, Fig. 2.5).
Foraging of Red-breasted Nuthatches was best predicted by the model which included
diameter/furrow depth, crown ratio, and tree species (logistic regression, x = 124.113,
N=718,/?<0.001; Table 2.14). The model was a useful one for predicting the use of trees
(ROC = 0.732). Trees that Red-breasted Nuthatches foraged upon had less live crown and
were larger in diameter and furrow depth than trees that were not used for foraging. Red­
breasted Nuthatches also foraged upon more Douglas-fir than was randomly available across
the treatment units (Table 2.15).
Four models, one which contained height/diameter, canopy connections, and crown
ratio (logistic regression, N=440, % = 43.453, p<0.001), one which contained
height/diameter, canopy connections, crown ratio, and tree species (logistic regression,

45

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Table 2.10. Comparison of models using the structural characteristics of trees to predict
the length of time White-breasted Nuthatches foraged upon them.
Model
4
1
7
8
2
5
3
6

Parameters Included
treatment
intercept
height + crown ratio + treatment
height + crown ratio
(global) treatment + height + dbh + furrow
depth + crown ratio
dbh + furrow depth + treatment
height + dbh + furrow depth + crown ratio
dbh + furrow depth

AICc
361.936
364.359
367.775
369.044
371.577

A AICc
0.000
2.423
5.879
7.108
9.641

Akaike Weight
0.7180
0.2137
0.0387
0.0205
0.0058

373.540
375.485
377.900

11.604
13.549
15.964

0.0022
0.0008
0.0002

Table 2.11. Parameter estimates (PE), standard error (SE), F-value, t-value, and pvalue of each variable within the best performing model using the structural
characteristics of trees to predict the length of time White-breasted Nuthatches foraged
upon them.
Variable
Intercept
Treatment
‘Control’
‘Thin’
‘Bum’
‘Thin and Bum’

PE
4.001

SE
0.142

-0.619
0.092
0.002
contrast

0.251
0.284
0.229

F
1538.111
2.564

p-value
t
28.162 <0.001
0.058
-2.462
0.015
0.324
0.746
0.011
0.992

46

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Table 2.12. Information criteria of candidate models used to predict the structural
characteristics of trees foraged upon by Pygmy Nuthatches.
Model

Parameters Included

p-value

AICc

6
4
2
13

diameter + crown ratio
diameter/furrow depth + crown ratio
tree size
tree size + crown ratio + canopy
connections
height/diameter + canopy
connections + crown ratio
height + canopy connections + crown
ratio
intercept

<0.001
<0.001
<0.001
<0.001

178.859
182.217
187.960
190.741

A AICc Akaike
Weight
0.000 0.833
3.358 0.155
9.101 0.009
11.882 0.002

<0.001

197.263

18.404

0.000

0.001

203.239

24.380

0.000

<0.001

216.895

38.036

0.000

10
8
1

Table 2.13. Parameter estimates (PE), standard error (SE), Wald value, and p-value of
each variable within the best performing model using the structural characteristics of
trees to predict foraging use by Pygmy Nuthatches.
Variable
Diameter
Crown Ratio

PE
0.112
0.004

SE
0.022
0.011

Wald
26.361
0.116

p-value
<0.001
<0.001

47

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U sed

m

1.00 —

m
o o

O bserved Value

o$
«b

O P redicted Value

0.80Vi

!=>
P 0.60-

©
I

•8 0.40“
O
A
0.2 0 -

o
fiP°
U nused 0 .0 0 '

10

30

40
!
Diameter (cm)

60

70

Figure 2.5: The probability that Pygmy Nuthatches would use a tree for foraging
increased as the diameter (cm) of the tree increased.

48

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Table 2.14. Information criteria of candidate models used to predict the structural
characteristics of trees foraged upon by Red-breasted Nuthatches.
A AICc

Model

Parameters Included

p -value AICc

5

diameter/furrow depth + crown ratio +
tree species
tree size + canopy connections + crown
ratio + tree species
height/diameter + canopy connections +
crown ratio + tree species
height/diameter + canopy connections +
crown ratio
height + canopy connections + crown
ratio + tree species
diameter/furrow depth + crown ratio
tree size + canopy connections + crown
ratio
height + canopy connections + crown
ratio
diameter + crown ratio + tree species
diameter + crown ratio
tree size + tree species
tree size
intercept

<0.001

875.818

Akaike
Weight
0.000 0.999

<0.001

890.446

14.628

<0.001

892.122

16.304 0.000

<0.001

897.689

21.871

0.000

<0.001

923.457

47.639

0.000

<0.001
<0.001

924.724
927.974

48.906 0.000
52.156 0.000

<0.001

939.626

63.808

0.000

<0.001
<0.001
<0.001
<0.001
1.000

976.026
997.082
1001.765
1043.467
1124.903

100.208
121.264
125.947
167.649
249.085

0.000
0.000
0.000
0.000
0.000

12
11
10
9
4
13
8
7
6
3
2
1

0.001

Table 2.15. Parameter estimates (PE), standard error (SE), Wald value, and />-value of
each variable of each variable within the best performing model using the structural
characteristics of trees to predict foraging use of Red-breasted Nuthatches.
Variable
Crown Ratio
Diameter/Furrow Depth
Tree Species

PE
-2.809
1.147
1.555

SE
0.604
0.118
0.227

Wald
21.603
94.454
46.758

p-value
<0.001
<0.001
<0.001

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2

N=440, x = 44.528, p<0.001), one which contained tree size, crown ratio, canopy cover, and
tree species (logistic regression, N=395, x = 44.603, p<Q.001), and the model which
included all predictors except tree species (logistic regression, N=395, % = 44.371, p<0.001),
were best at predicting tree use by White-breasted Nuthatches (Table 2.16). Both models had
poor predictive accuracy (ROC = 0.672-0.676). White-breasted Nuthatches foraged upon
trees that were larger, and with less live crown than trees that were not foraged upon (Table
2.17).

2.4.3. Structural Differences Among Trees Within Each Treatment Unit
Stand and tree structure differed among treatment types at the Hungry Bob research
area (Table 2.18). Many variables measured (diameter, height, furrow depth, # of Douglasfir) were similar between ‘control’ and ‘thin’, and ‘bum ’ and ‘thin and bum’. ‘Thin and
bum ’ was similar to ‘control’ only in the # of ponderosa pine within the treatment units.

2.4.4. Foraging Behavior Differences between Treatments
The proportion of time that birds were observed in behaviors other than foraging for
food was not significantly different among treatments for Pygmy Nuthatches (KruskalWallis, N=26, 77=1.29, p=0.731), White-breasted Nuthatches (Kruskal-Wallis, N=50,
77=2.41, p=0.476), or Red-breasted Nuthatches (Kmskal-Wallis, N=101, 77=1.59, p=0.662).
The proportion of foraging time that zones of the tree were used did not differ along a
horizontal axis (bole, proximal branches, or distal branches) or along a vertical axis (top,
middle, or bottom) among treatments for any species of nuthatch (Table 2.19 and 2.20). For
Pygmy Nuthatches, there were too few observations in both ‘thin’ and ‘bum’ treatments to

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Table 2.16. Information criteria of candidate models used to predict the structural
characteristics of trees foraged upon by White-breasted Nuthatches.
Model Parameters Included
13
10
12
11
9
8
6
7
5
4
2
3
1

tree size + canopy connections + crown
ratio
height/diameter + canopy connections +
crown ratio
tree size + canopy connections + crown
ratio + tree species
height/diameter + canopy connections +
crown ratio + tree species
height + crown ratio + canopy connections
height + crown ratio + canopy connections
+ tree species
diameter + crown ratio
diameter + crown ratio + tree species
diameter/furrow depth + crown ratio + tree
species
diameter/furrow depth + crown ratio
tree size
tree size + tree species
intercept

A AICc

p -value

AICc

<0.001

511.285

Akaike
Weight
0.000 0.411

<0.001

512.203

0.918

<0.001

513.114

1.829 0.165

<0.001

513.189

1.904

0.159

<0.001
<0.001

520.721
521.912

9.436
10.627

0.004
0.002

<0.001
<0.001
<0.001

558.014
559.447
572.108

46.729 0.000
48.162 0.000
60.823 0.000

<0.001
<0.001
<0.001
1.000

572.425
582.381
584.403
611.979

61.140
71.096
73.118
100.694

0.260

0.000
0.000
0.000
0.000

Table 2.17. Parameter estimates (PE), unconditional standard error (USE), and
confidence intervals (Cl) of each variable, derived by model averaging, using the
structural characteristics of trees to predict foraging use of trees by White-breasted
Nuthatches.
Variable
Crown Ratio
Diameter/Height
Canopy Connections
Tree Species
Tree Size

PE
-0.019
0.731
0.065
0.262
0.736

USE
0.007
0.127
0.097
0.363
0.127

Lower 95% Cl Upper 95% Cl
-0.005
-0.033
0.482
0.979
-0.124
0.255
-0.450
0.975
0.487
0.985

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Table 2.18. Differences in vegetation structure among treatment types. Values sharing
letters are not statistically different at an alpha level <0.05. *represents the average # of
ponderosa pine and Douglas-fir within 4002 meters centered on each grid marker.
Variable

Control Thin

Bum

Thin and
Bum

yt

N

/7-value

Diameter (cm)

17.8a

17.2 a

24.8 b

25.0b

292.52

3921

<0.001

Height (m)

12.0 a

11.4 a

14.9 b

15.2 b

183.40

3921

<0.001

Crown Ratio (%)

50.5 3

43.6b

43.5 b’C 39.8°

131.05

3908

<0.001

Canopy
21.4 3
Connections (%)
Furrow Depth (mm) 11.6 a
*Ponderosa Pine (#) 11.2 3

10.6 b,C

10.8 b

7.5 C

78.28

1212

<0.001

11.5 a

13.0 b

13.5 b

37.54

1212

<0.001

9.6 a

9.6 a

6.8 a

3.51

297

0.319

*Douglas-fir (#)

6.3 a

1.4 b

i.ob

68.88

297

<0.001

8.4 a

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Table 2.19. Results of Mann-Whitney V-tests used to compare the amount of time that
Pygmy Nuthatches spent foraging within different zones among treatments.
Zone
N
Top
49
Middle
Bottom
Bole
Proximal
Distal

U value
242.500
250.000
186.500
225.000
251.500
183.000

p-value
0.786
0.914
0.137
0.515
0.939
0.118

Table 2.20. Results of Kruskal-Wallis H-tests used to compare the amount of time that
Red-breasted and White-breasted Nuthatches spent foraging within different zones
among treatments. RBNU=Red-breasted Nuthatch and WBNU=White-breasted
Nuthatch.
Bird Species
RBNU

WBNU

Zone
top
middle
bottom
bole
proximal
distal
top
middle
bottom
bole
proximal
distal

N
213

H value
0.335
7.356
6.918
3.396
0.434
5.855
7.718
8.376
8.928
4.773
6.574
3.300

83

p-value
0.953
0.061
0.075
0.335
0.933
0.119
0.052
0.039
0.030
0.189
0.087
0.348

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allow comparison, so a Mann-Whitney U test was used to compare ‘control’ and ‘thin/bum’
units.

2.5. Discussion
The density of individuals in an area has been linked to fecundity and food
availability and thus to habitat quality for avifauna (Enoksson and Nilsson 1983, Sergio and
Newton 2003). Pygmy Nuthatches were observed less frequently in ‘thin’ units and ‘bum ’
units, than in ‘thin and bum’ treatment units (Fig. 2.2). ‘Thin and bum’ treatment units had
trees with fewer canopy connections than trees in any other treatment (Fig. 2.18). Pygmy
Nuthatches may prefer forests with less than 70% canopy closure (Baida et al. 1983, Csuti et
al. 1997, Kingery and Ghalambor 2001). Fewer White-breasted Nuthatches were observed in
the ‘control’ units than in ‘thin and bum ’ treatment units. The abundance of Red-breasted
Nuthatches was not different between treatment types at the Hungry Bob research area.
However, abundance differences were found after forest thinning and burning in other areas
(Adams and Morrison 1993, Hagar et al. 1996, Artman 2002, Siegel and DeSante 2003). The
selection criteria of habitat may vary by spatial scale for foraging birds. Red-breasted
Nuthatches were more common on a landscape scale than the other two species of nuthatch
studied at Hungry Bob. Territory boundaries may therefore confine nuthatches to a particular
area (Hutto 1985, Allen et al. 1987). Perhaps competition for territories prevented Red­
breasted Nuthatches from immigrating to other areas in response to treatment type, so
instead, they altered their foraging behavior. This hypothesis could be tested by following a
population of banded birds in order to determine: dominance hierarchy of neighbors, settling
date of territories, and territory size (Enoksson and Nilsson 1983, Nilsson 1987). Taking
these steps could eliminate one other possibility, that the increased foraging rate of Red-

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breasted Nuthatches in ‘thin’ units influenced the encounter rate between the nuthatches and
field observers, masking a difference in the abundance of the birds.
Red-breasted Nuthatches spent more time foraging on each tree in ‘thin and bum ’
units than in ‘thin’ or ‘control’ treatment units (Fig. 2.3, Fig. 2.4). They also spent more time
on trees in ‘bum ’ treatments than ‘thin’ treatments. The other two species of nuthatch were
not different in the amount of time they spent on each tree among treatments. According to
the marginal value theorem, birds should leave trees sooner in areas where food resources are
rich (Chamov 1976). In contrast, the rate of travel for foraging birds has been shown to be
inversely proportional to resource abundance, including food and cover (Morrison et al.
1989, Olsson et al. 2001). The difference may be that the marginal value theorem fails to
take into account: increased predation risk of traveling between trees (Post and Gotmark
2006), interspecific competition for food (Stallcup 1968), and assumes that resources are
equal on all trees.
Arthropod populations were not adversely affected by prescribed fire in oak
(Quercus)-savannah habitats (Siemann et al. 1997) or longleaf pine (Pinus palustris) habitats
(Taylor 2003). More bark-surface arthropods, and more arthropod species, were found in
areas that had been disturbed by fire than areas that had not (Volker 1991). Many arthropods
found on the bark of trees actually migrate there from the leaf litter layer (Apigian et al.
2006). The community structure of arthropods in the leaf litter layer was more affected by
fire than thinning in the Sierra Nevada, but the effects on arthropod density were taxaspecific and moderate (Apigian et al. 2006).
Longer durations of time spent foraging upon each tree may indicate a greater
abundance of food on that substrate (Morrison et al. 1989). The models that performed best

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for predicting the amount of time that nuthatches would stay upon trees while foraging did
not include any structural variables for either Red-breasted or White-breasted Nuthatches.
Adams and Morrison (1993) also failed to find a correlation between structural attributes of
foraged trees and time spent on the trees foraging.
All species of nuthatch exhibited preference between structural characteristics of trees
that were used for foraging, and trees that were not used. Comparison of the models used to
predict use of trees for foraging by nuthatches revealed differences in model performance
among nuthatch species. Because of the nature of regression analyses, the regression models
found a significant difference between trees used for foraging and those not used only when
the preferred structure was not the average condition in the stand (Dodge et al. 1990).
Therefore, these results should be interpreted not as absolute models of tree structure
preferences of nuthatches, but as an identification of preferences that were outside of the
average condition found on each treatment unit. From model selection alone, it would seem
that trees deviated from the desired condition in the fewest structural attributes for Pygmy
Nuthatches. Pygmy Nuthatches were also nearly restricted to ‘control’ and ‘thin and bum’
areas, indicating that they are more selective in the habitat they occupy than the other two
species. Differences in the structural characteristics of trees among treatment types (Fig.
2.18) do not entirely dictate the abundance of each nuthatch species in each treatment unit.
For example, Red-breasted Nuthatches selected Douglas-fir more frequently for foraging
than it was randomly available at Hungry Bob. ‘Bum’ and ‘thin and bum’ units had less
Douglas-fir than ‘control’ or ‘thin’ units, however, there was no difference in the number of
encounters of Red-breasted Nuthatches among units.

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Variables measuring tree size were always significant predictors of foraging use by
nuthatches. Bark furrow depth has been positively linked to the abundance and size of barksurface arthropods (Volker 1989, Adams and Morrison 1993). A preference by barkforaging birds for larger trees has been found in most studies where it has been tested,
perhaps simply due to increased surface area for foraging (Morrison et al 1987, Weikel and
Hayes 1999).
Trees with less live crown covering the bole were more likely to be foraged on by
Red-breasted Nuthatches and White-breasted Nuthatches. Birds may prefer to forage upon
sections of the bole that are not covered by foliage in these treatments. The percent of the
crown free from contact with the rest of the canopy was not significant in logistic regression
models to predict which trees nuthatches would use for foraging. Trees with a greater
proportion of connections to the canopy were used more in mixed-coniferous forests of
Oregon (Weikel and Hayes 1999), presumably because birds could use crown connections to
travel between trees while foraging in the canopy. However, adjacent trees may not fulfill
the strong structural preferences demonstrated by nuthatches, negating the use of canopy
connections to travel between foraging substrates.
If food were more limiting in one treatment than another, one would expect that
nuthatches would have to spend more time foraging in the treatment where food was more
limiting — especially since foraging effort has been linked to predation risk in Eurasian
Blackbirds (Turdus merula; Post and Gotmark 2006). Non-foraging behaviors were not
observed more or less frequently in any treatment for any species. Research on foraging
dynamics and population density has indicated that food is not limiting for birds in ponderosa
pine (Brawn 1987, Brawn et al. 1987, Brawn and Baida 1988a). Nuthatches habitually cache

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food items in bark crevices of trees (Heinrich et al. 1997), confounding the interpretation of
the amount of time spent foraging as an indication of food availability.
Red-breasted Nuthatches selected only the heaviest seeds at feeders (Heinrich et al.
1997), demonstrating that these birds are selective in the food resources they choose, even
when in general those resources are abundant. An alteration in the use of foraging zones
depending on treatment type might indicate a disparity in prey abundance in different areas
of the trees, and an adaptation by nuthatches to this variation in food resources (Block 1990,
Sallabanks 1993). Nuthatches did not alter their use of vertical or horizontal axes among
treatments. In a study of geographic variation in foraging behavior, nuthatches were less
plastic in their foraging behavior than most species, with Pygmy and White-breasted
Nuthatches scoring lower than Red-breasted Nuthatches (Petit et al. 1990). However, White­
breasted Nuthatches showed the greatest diversity of prey selection in pine forests of Oregon,
when compared to either Pygmy or Red-breasted Nuthatches (Anderson 1976). As generalist
and opportunistic insectivores, Red-breasted Nuthatches are found in a much wider range of
habitats than either Pygmy or White-breasted Nuthatches (Ghalambor and Martin 1999).
Pygmy Nuthatches may be the most highly specialized of the foragers in this study, and
therefore, the most sensitive to changes in vegetation structure caused by restorative
treatments. This is illustrated by the paucity of individuals detected in any unit where ‘thin’
or ‘bum ’ were applied.
In general, the results of this research indicate that thinning combined with burning
increases use of the area by White-breasted and Pygmy Nuthatches. Burning or thinning
alone appeared to alter foraging habitat little for Red-breasted and White-breasted
Nuthatches; however, Pygmy Nuthatches seem to disappear in habitats where thinning or

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burning alone are applied. In ponderosa pine forests of Arizona, no population change was
reported for Pygmy or White-breasted Nuthatches after prescribed fire was applied to the
area (Horton and Mannan 1988, Machmer 2002). The failure of the analyses reported here,
to find an increase in detection rate between ‘control’ and ‘bum’ treatments, indicates that
the combination of thinning and burning impacts habitat quality differently than thinning or
burning alone.
There is a variation in foraging behavior by birds that occurs: between years in
ponderosa pine ecosystems (Szaro et al. 1990); between months for other bark-gleaning birds
(Hejl and Vemer 1990); between stages of the breeding cycle (Sakai and Noon 1990) and;
between sexes (Grubb and Woodrey 1990, Hanowski and Niemi 1990), ages, or dominance
status of the birds (Grubb and Woodrey 1990). The research reported in this thesis was not
designed to take into account these variations. Models with greater complexity than those
presented here may capture more of the error inherent in each model. For example, density
estimates alone without a measure of individual reproductive success or survivorship, fail to
differentiate high-quality territories from ecological sinks that are attractive to low-quality or
first-year breeding pairs (Smallwood 2001). An analysis of nesting abundance and success is
necessary to determine whether the frequency of encounters of foraging individuals was due
to foraging habitat alone, or nesting habitat differences between treatments.

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3. The effects of restorative treatments in ponderosa pine on nesting ecology of Red­
breasted (Sitta canadensis) and Pygmy (Sitta pygmaea) Nuthatches
3.1. Abstract
Fire exclusion, logging, and other management practices have changed the
composition and structure o f historic ponderosa pine (Pinus ponderosa,) ecosystems. As a
result, ponderosa pine habitats are now more susceptible to stand-replacing fire. Mechanical
thinning and prescribed burning have both reduced the risk o f crowning fire when applied to
forests; however, their effects on avian nesting ecology are poorly understood. Three
restorative treatments ( ‘thin ’, ‘burn ’, and ‘thin and burn ’) and ‘control’ were applied to
ponderosa pine forests within northeastern Oregon. The effects o f these restorative
treatments upon the daily nest survival, nest density, and nest structural characteristics o f
Red-breasted (Sitta canadensis,) and Pygmy (S. pygmaea,) Nuthatches were determined by
finding and monitoring nests and comparing differences among treatments and controls. The
success o f Red-breasted Nuthatch nests was not significantly different among treatment
types. Models o f nest survival containing diameter o f the nest tree, nest height, and canopy
cover performed poorly. Models o f daily nest survival that included structural characteristics
o f nest trees o f Pygmy Nuthatches did not perform better than a constant estimate o f daily
nest survival. There were fewer nests o f Red-breasted Nuthatches within ‘thin and burn ’
treatment units than were expected. Red-breasted Nuthatches nested within snags that had
less canopy cover and more snags within an 11.3 m radius. Pygmy Nuthatches nested within
snags with a larger diameter than that most commonly available. Further research on
nesting behavior that incorporates provisioning rates, fecundity, or settling date o f territories
may improve our understanding o f the effects o f restorative treatments on the nesting ecology
o f nuthatches.

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3.2. Introduction
Fire suppression initiatives within North America, combined with logging, grazing,
and other forest management practices, have contributed to the loss of ecosystems with
historic fire-regimes that were high-frequency and low-severity, such as ponderosa pine
ecosystems (Allen et al. 2002; Brown et al. 2004). Increased fire-retum intervals within
these western forests have created forests that are more dense and uniform in their stem
dispersion (Mast et al. 1999), and have fewer large old trees and more small young trees
(Swetnam 1990, Mast et al. 1999). These changes in forest composition and structure have
shifted the fire regime from frequent understory fires to infrequent, crowning wildfires to
which ponderosa pine forests and their associated organisms are not adapted (Agee 1996).
Mechanical thinning and prescribed burning have both been responsible for decreasing fire
intensity when they are applied to ponderosa pine forests (Pearson et al. 1972, Pollet and
Omi 2002). Restoration methods will vary according to the extent of deviation from
reference (historic) conditions, and other factors such as economic interests and climate
change (Moore et al. 1999).
The effects of various restorative treatments within ponderosa pine on biological
aspects of ecosystem function, such as avian nesting dynamics, are poorly understood.
Maintaining a population of primary cavity-nesting birds ensures the creation of suitable
nesting and roosting habitat for a number of cavity-dwelling bird and mammal species (Bate
et al. 1999, Aitken et al. 2002). Each excavating species tends to create cavities with different
qualities (depth, entrance width, volume, height on bole, distance to edge habitat edge, decay
type and extent, etc). Therefore, the diversity of cavity-excavators can influence the diversity
of secondary-cavity-nesters in an ecosystem (Brawn and Baida 1988a). Three species of

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cavity-excavator present within the Blue Mountains of Oregon are nuthatches: White­
breasted (S. carolinensis), Red-breasted, and Pygmy. Few studies have documented the
effects of restorative treatments on the nest-site selection and nest density of nuthatches. The
objectives of this research are to 1) compare the density of nuthatch nests among control and
restorative treatments, 2) model daily nest survival among restorative treatments and control
units for Red-breasted Nuthatches, and 3) report on the nest-site structural characteristics of
nest trees used by Pygmy and Red-breasted Nuthatches within ponderosa pine forests of
northeastern Oregon.
3.3. Methodology
3.3.1. Study Site
The Hungry Bob study site was located in the Blue Mountains of northeastern
Oregon, within the Wallowa-Whitman National Forest (45° 37’ N, 117° 15’ W). Please see
section 1.4. for a detailed description of the Hungry Bob site.
3.3.2. Treatments and Study Units
Four treatments were included in the study design (prescribed burning only -‘bum ’,
mechanical thinning only -‘thin’, mechanical thinning followed by prescribed burning -‘thin
and bum ’, and no treatment - ‘control’). Four replicates of each treatment were created,
totaling 16 experimental units. For more details about the placement of treatments, please
see section 1.4.

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3.3.3. Nest-site Preferences
Twelve experimental study units were randomly selected in which to search for
Pygmy and Red-breasted Nuthatch nests during 2003 and an additional 3 in 2004. Research
was conducted during the breeding season of nuthatches at the latitude of the study sites,
which was typically from the beginning of May through the end of July. Field research
began by the 21st of April and ended when all known nests had fledged or failed.
All snags within each unit were searched for cavities. Upon discovery of a cavity, the
snag was monitored for at least 30 minutes at least once per week for the first month of the
breeding season. Also, research units were walked systematically twice per week for 2-3
hours at a time. If a bird exhibiting nesting behavior (i.e., holding food in its bill, collecting
lichen or twigs, dumping shavings from its bill) was observed, it was followed back to its
nest (Martin and Geupel 1993). Also, excavation noises and territorial songs were followed
within areas where nests had not been discovered.
Nest monitoring methods were based on techniques standardized by the Breeding
Bird Field Protocol (BBIRD) established in 1997 by the Institute of Bird Populations
observed (Martin et al. 1997), and modified according to Dudley and Saab (2003). Nests
were watched once every 3 days for 45 minutes, or until nest activity was confirmed.
Behavioral cues that were used to confirm nest activity included an adult bird bringing food
to the nest and leaving without it, or hearing begging of nestlings within the nest cavity. If
no activity was seen at a nest, it was visited an additional 3 times before nest fate (fledge or
failure) was declared. Nest fating decisions were made according to standards set forth by
Martin et al. (1997). In example, if the nest was estimated to be within 2 days of fledging

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between the last two visits to the nest, and the nest was empty on the last nest check, the nest
was assumed to have fledged young.
To minimize the risk of observer-induced depredation of nests, some precautions
were taken according to the advice of Martin and Geupel (1993). The observers immediately
moved away from the nest if met with agitation from the parent birds during nest-checks.
Flagging marking the nest-check location was then placed more distantly to prevent the same
stress during subsequent nest checks. See Figure 3.1 as an example of a nest-observation
location. The observer moved away from the nest upon sight of a nest predator. A quick
check for nest predators was conducted before attempting to approach or check a nest. A
comment was written whenever an observer saw a nest predator within the same tree as a
nest. Observers never left a dead-end trail to any nest, or even a nest observation site. A
different route away from the nest was used on each visit whenever possible.
Once the fate of each nest was established (i.e., fledge or failure), an 11.3 m radius
(0.04 ha) was surveyed around the nest to determine microhabitat characteristics. Vegetation
data were gathered based on methods used by James and Shugart (1970) and Noon (1981),
and revised according to Anderson and Crompton (2002). Species, height category, and
diameter category of all trees greater than 1.3 m in height were recorded. The density of
canopy cover was estimated using an ocular tube. At all nest sites, measurements of canopy
cover were taken along two transects, one running east from the nest tree and one running
north from the nest tree (these compass points were selected randomly at the start of the
season). One measurement was taken with the ocular tube every 2nd m along each transect,
which yielded 6 measurements. Height, diameter at breast height (dbh), and decay class
(Bull et al. 1997) of all snags within the survey area (including the nest tree) were quantified.

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Figure 3.1: Example of a typical nest observation site on the Hungry Bob research
units. The nest is indicated by a white arrow. The picture was taken with a 35mm lens
from the nest observation location.

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To make a comparison between the snags that were chosen for nesting and the snags
available within each treatment unit, a survey of snags was conducted. All snags located
within each treatment unit within decay classes two and three and over 11 cm in diameter
were surveyed in the same manner as nest trees. Trees within these structural parameters
were the most likely to be used as nest-sites by nuthatches (Ghalambor and Martin 1999).
This method allowed comparisons of available snags among treatment units (Martin and Li
1992, Sherry and Holmes 1992), which aided in connecting nest usage to specific structural
characteristics on the nest-tree and microhabitat scale (Martin 1988, Knopf et al. 1990, Ralph
et al. 1993).
3.3.4. Analysis
Daily nest survival rates of Red-breasted Nuthatch nests were calculated using
logistic exposure models (Shaffer 2004). All continuous variables that were hypothesized to
influence the nest success of cavity-nesting birds (treatment, dbh of the nest tree, nest height,
and average canopy cover within 6 m of the nest tree) were modeled separately because of
sample size limitations. Daily survival estimates were linked to covariate measures using a
logit link, which is most appropriate for binomial distributions such as nest survival (Rotella
et al. 2004). Akaike’s Information Criterion adapted for small sample sizes (AICc) was used
in order to select the best-fitting of the candidate models (Hurvich and Tsai 1989, Burnham
and Anderson 2002, Table 3.1). Unlike the Mayfield method (Johnson 1979), logistic
exposure analysis allows each nest to have unique covariate values and permits variability in
daily nest survival.
Chi-square goodness-of-fit tests were used to compare the total number of nests of
Red-breasted Nuthatches among treatments and then to compare the number of potential

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Table 3.1. Candidate models to predict the structural characteristics of snags that
nuthatches nested within.
Model Number
1
2
3
4
5

Factors Included
(global) height + canopy cover + diameter + decay class + # of snags
height + canopy cover + diameter
diameter + decay class
# of snags + diameter
intercept

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nesting snags among treatments (Siegel and Castellan 1988). Nonparametric tests were used
because these count data were not normally distributed.
Nest-site structural characteristics and microhabitat measurements of nest-trees and
non-nest-trees were compared using logistic regressions in order to determine which
variables were important in separating nest snags from non-nest snags (Agresti 1990, Trexler
and Travis 1993, Steeger and Hitchcock 1998). Candidate models were developed based on
what the literature has shown affects cavity-nesting birds’ choice of nest site (Table 3.1).
Cavity nests placed higher with little canopy cover around them are depredated less often
(Rendell and Robertson 1989, Pingjun and Martin 1991). Nests in a more advanced state of
decay and with a larger diameter are easier to excavate (Swallow et al. 1986). Cavity-nests
placed within trees surrounded by other snags provide a choice of nesting locations within a
single territory. Diameter is nearly always an important factor in nest-location for cavitynesting birds, so it is included within all models (Harestad and Keisker 1989, Dobkin et al.
1995). Candidate models were compared using Akaike’s Information Criterion corrected for
small sample sizes (AICc, Hurvich and Tsai 1989, Burnham and Anderson 2002). Predictive
ability of models were assessed using reciever operating characteristic (ROC) scores (Zweig
and Campbell 1993). Models with ROC scores exceeding 0.70 were considered useful
models (Swets 1988, Manel et al. 2001).
Analyses were run using SPSS (Version 14, 2005), MINITAB (Version 14, 2003),
and SAS (Version 9.1.3, 2003). Post-hoc multiple comparisons for Kruskal-Wallis tests were
done using methods described in Siegel and Castellan (1988). The alpha level for each test
was set at 0.05. Cases with standardized residuals >2.58 or <-2.58 and Cook’s distance of < 1
were eliminated as outliers within analyses.

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3.4. Results
A total of 67 Red-breasted Nuthatch and 13 Pygmy Nuthatch nests were found in the
2 breeding seasons of the study. Rigorous definitions for nest fating decreased the samples
used in modeling daily nest success to 15 Red-breasted Nuthatch nests and 11 Pygmy
Nuthatch nests. Of the nests used in the analysis, 5 Red-breasted and 3 Pygmy Nuthatch
nests failed during the course of nest monitoring. The constant daily nest survival rate of
Red-breasted Nuthatches and Pygmy Nuthatches at the Hungry Bob research units was
0.993. Models with single continuous variables performed as well as the constant estimate of
daily nest survival of Red-breasted Nuthatches (Delta AICc < 2, Burnham and Anderson
2000; Table 3.2). Snags with a greater dbh, greater canopy cover, and higher nests tended to
have higher daily nest survival (Table 3.3, Figures 3.2-3.4). Small sample sizes prohibited
the analysis of treatment type in modeling daily nest survival for Pygmy Nuthatches. The
model containing canopy cover performed as well as the constant daily survival estimate for
Pygmy Nuthatches in the Hungry Bob research area (Logistic exposure, N=358,
AICc=80.073, Table 3.4). Daily survival of Pygmy Nuthatch nests tended to decrease with
increased canopy cover (Table 3.5, Figure 3.5).
There was a difference in the number of Red-breasted Nuthatch nests found in each
treatment (chi-square goodness-of-fit test, df=3,

= 8.353, p<0.05; Figure 3.6). Post-hoc

comparisons of the chi-square values indicated that fewer nests were found within ‘thin and
bum ’ treatment units than were expected (Sokal and Rohlf 1994). Sample sizes were
insufficient to compare the number of nests of Pygmy Nuthatches among treatment types
(Fig. 3.7). The number of snags available and superficially appropriate for excavation by

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Table 3.2. Information criteria of candidate models used to model daily nest survival of
Red-breasted Nuthatches within Hungry Bob.
Model
Number
1
3
2
4
5

Parameters Included

AICc

A AICc

intercept
diameter of nest tree
nest height
canopy cover around nest tree
treatment

26.948
27.580
28.216
28.905
28.949

0.000
0.633
1.269
1.958
2.002

Akaike
Weight
0.333
0.243
0.177
0.125
0.122

Table 3.3. Parameter estimate (PE), standard error (SE), and 95% confidence intervals
(Cl) of nest-tree structural variables in predicting nest success for Red-breasted
Nuthatches.
Variable
Intercept
Diameter
Canopy Cover
Height
Treatment

PE
5.021
0.105
0.010
0.153
-0.236

SE
0.449
0.067
0.026
0.137
0.916

Lower 95% Cl
4.142
-0.026
-0.042
-0.116
-2.031

Upper 95% Cl
5.901
0.236
0.062
0.422
1.559

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1.0000
s

0.9995

!Z5

0.9990
0.9985
0.9980
0.9975

20

10

30

50

40

Dbh (cm)
Figure 3.2: Daily nest survival of Red-breasted Nuthatches increased as diameter
increased.

1.0000
? 0.9990
|
2 0.9980
cn

£
0.9970
0.9960
0.9950
0.9940
0

5

10

15

20

25

30

35

Nest Height (m)

Figure 3.3: Daily nest survival of Red-breasted Nuthatches increased as nest height
increased.

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Estimated Daily Nest Survival

1.0000
0.9990
0.9980
0.9970
0.9960
0.9950
0.9940
0.9930
0

20

40

60

80

100

Average Canopy Cover (%)
Figure 3.4: Daily nest survival of Red-breasted Nuthatches increased as canopy cover
increased.

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Table 3.4. Information criteria of candidate models used to model daily nest survival of
Pygmy Nuthatches within Hungry Bob.
Model
Number
1
4
3
2

Parameters Included

AICc

A AICc

(null) intercept
canopy cover around nest tree
diameter of nest tree
nest height

16.102
17.186
18.103
18.139

0.000
1.084
2.001
2.037

Akaike
Weight
0.433
0.252
0.159
0.156

Table 3.5. Parameter estimate (PE), standard error (SE), and 95% confidence intervals
(Cl) of nest-tree structural variables in predicting nest success for Pygmy Nuthatches.
Variable
Intercept
Canopy Cover
Diameter
Height

PE
4.879
-0.058
-0.016
-0.027

SE
0.580
0.043
0.043
0.104

Lower 95% Cl
3.683
-0.142
-0.101
-0.231

Upper 95% Cl
5.955
0.026
0.069
0.177

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Estimated Daily Nest Survival

1.0000
0.9950
0.9900
0.9850
0.9800
0.9750
0.9700
0.9650
0.9600
0.9550
0

20

40

60

80

100

Average Canopy Cover (%)
Figure 3.5: Daily nest survival of Pygmy Nuthatches tended to decrease as canopy cover
increased.

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C o n tro l

T h in

B um

T h in a n d
B um

Treatm ent type
Figure 3.6: The number of nests of Red-breasted Nuthatch found within each treatment
type and each year.

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Number of nests

6

5

12003
12004

0

Control

T hin

B um

Thin and B um

Treatment type
Figure 3.7: The number of Pygmy Nuthatch nests found within each treatment type and
each year.

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nuthatches was different am ong treatm ent types (chi-square goodness-of-fit test, df=3,

=

13.559, p<Q.05; Table 3.6); fewer snags were found within ‘thin and bum ’ units, and more
snags were found within ‘bum ’ treatments, than expected.
Logistic regression models were able to use structural variables and microhabitat
characteristics to predict which trees would be used for nesting by Red-breasted Nuthatches
(Logistic regression, N=144, y;2 = 127.682, p<0.001; Table 3.7). The model had acceptable
predictive accuracy (ROC = 0.762). Snags with nests of Red-breasted Nuthatches had less
canopy cover and more snags within 11.3 m than snags without nests (Table 3.8). No other
variables were significant within the model. Logistic regression models were able to use
structural variables and microhabitat characteristics to predict which trees would be used for
nesting by Pygmy Nuthatches as well (ROC model 4 = 0.812, ROC model 2 = 0.867; Table
3.9 and 3.10; Figure 3.8).

3.5. Discussion
The number of nests of Red-breasted Nuthatches differed among treatments (Fig.
3.6). This does not agree with research in prescribed bums in southeastern Arizona, where
the nest-density of Red-breasted Nuthatches did not differ between treated areas and controls
(Horton and Mannan 1988). There were about half as many snags with characteristics most
likely to provide suitable nesting habitat (decay classes 2-4 and >11 cm dbh) in ‘thin and
bum ’ treatment units than in any other treatment or control (Table 3.6). Competition for nest
sites might be more significant for cavity nesters than selection between possible nest-sites
when the resource is limiting (Martin et al. 2004).

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Table 3.6. The number of snags within decay classes 2, 3 or 4 and over 11 cm in
diameter within each treatment type.
# of Snags

Control
40

Thin
37

Bum
48

Thin and Bum
18

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Table 3.7. Information criteria of candidate models to predict the structural
characteristics of snags that Red-breasted Nuthatches nested within.
Model

Parameters Included

p -value

AICc

1

(global) height + canopy cover +
diameter + decay class + # of
snags
diameter + decay class
height + canopy cover + diameter
# of snags + diameter
(null) intercept

<0.001

140.295

A AICc Akaike
Weight
0.000
0.999

0.047
0.042
0.091

153.941
157.488
158.776
159.436

13.646
17.193
18.481
19.141

3
2
4
5

0.001
0.000
0.000
0.000

Table 3.8. Parameter estimate (PE), standard error (SE), and p-value of nest-tree
structural variables in predicting which snags were used for nesting by Red-breasted
Nuthatches.
Variable
Canopy Cover
# Snags
Decay Class
Decay Class 1
Decay Class 2
Decay Class 3
Height
Diameter

PE
-0.053
0.183

SE
0.016
0.054

1.275
2.179
1.041
0.040
0.009

1.229
1.124
1.073
0.047
0.022

Wald
11.140
11.715
6.742
1.077
3.756
0.941
0.722
0.171

p-value
0.001
0.001
0.081
0.299
0.053
0.332
0.396
0.679

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Table 3.9. Information criteria of candidate models to predict the structural
characteristics of snags that Pygmy Nuthatches nested within.
Model

Parameters included

p-value

AICc

4
2
5
1

# of snags + diameter
height + canopy cover + diameter
(null) intercept
(global) height + canopy cover +
diameter + # snags

0.018
0.031

35.521
37.470
38.659
43.696

0.061

A AICc Akaike
Weight
0.000
0.624
1.949
0.236
3.138
0.130
8.174
0.010

Table 3.10. Parameter estimate (PE), standard error (SE), and confidence interval (Cl)
of nest-tree structural variables in predicting which snags were used for nesting by
Pygmy Nuthatches. * Indicates a variable that appeared within more than one model,
so all information has been derived from model averaging.
Variable
*Diameter
Canopy Cover
Height
# Snags

PE
0.065
0.007
0.071
0.066

SE
0.033
0.038
0.081
0.144

Lower 95% Cl
0.130
0.081
0.230
0.348

Upper 95% Cl
0.001
-0.067
-0.088
-0.216

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Us ed

• • ••

1.00-

8 P O bserved Value

O Predicted Value

0.80-

v / 'P r e d i c t e d Value

<n

K
S3

9*
£ 0.60(A

s
<*o-!
1 “ 0.40-

■8
i-2

O
0. 2 0 -

•• •

U nused

••

i— r
15

20

25

30

35

40

45

50

55

65

70

75

Diameter (cm)

Figure 3.8: The probability of a snag being used for nesting by Pygmy Nuthatches
increased as the diameter (cm) of the snag increased. The y-axis represents both the
observed value of nest use and the value predicted by the logistic regression model.

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Though not statistically significant, no nests of Pygmy Nuthatches were found in
‘thin’ treatment units (Fig. 3.7). Thinning has decreased numbers of Pygmy Nuthatches in
other areas as well (Hejl 1994). Pygmy Nuthatches are more restricted in their habitat
requirements than Red-breasted Nuthatches, yet they occupy more diverse nest-sites
(McEllin 1979, Brawn 1987, Wisdom et al. 2000). Pygmy Nuthatches were often able to
excavate the bark layer of ponderosa pine and nest between the loose bark and the bole of the
tree within the Hungry Bob research units. They were also found within natural cavities,
while Red-breasted Nuthatches occupied only excavated cavities at Hungry Bob.
Density estimates alone without a measure of individual reproductive success or
survivorship fails to differentiate high-quality territories from ecological sinks that are
attractive to low-quality or first-year breeding pairs (Smallwood 2001). There was no
difference in daily nest survival of Red-breasted Nuthatches in different treatment types
(Table 3.2). Similarly, nest success was not influenced by thinning in mixed conifer stands
in the Sierra Nevada (Siegel and DeSante 2003) or pine stands in Arkansas (Barber et al.
2001 ).

Daily survival of nests of Red-breasted Nuthatches tended to increase as diameter of
the tree (Fig. 3.2) and height of the nest (Fig. 3.3) increased. Other studies have documented
higher success with these characteristics as well (Pingjun and Martin 1991, Christman and
Dhondt 1997, Spiering and Knight 2005). Daily nest survival tended to increase with
increased average canopy cover around the nest-site for Red-breasted Nuthatches (Fig. 3.4).
This association has been seen for open-cup nesters, however, cavity-nesting species
generally rely on vigilance to prevent nest failure due to depredation and so usually prefer
less cover around the nest-site (Martin and Roper 1988, Nilsson 1984, Finch 1989, Li and

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Martin 1991). Daily survival of Pygmy Nuthatch nests showed the opposite trend with
respect to canopy cover, as their success tended to decrease with increased canopy cover
(Fig. 3.5). Pygmy Nuthatches are sensitive to stand-level canopy cover, exclusively
inhabiting stands with less than 70% canopy cover on average within some areas (Baida et al.
1983, Csuti et al. 1997, Kingery and Ghalambor 2001). Associations between habitat and
nest-site structure and daily nest survival were weak within Hungry Bob, however, and all
95% confidence intervals of parameter estimates included zero. Martin (1998) found that
birds were selective in nest placement, and nests within areas with habitat structures that
were most often used by the birds were more successful than nests placed in other areas.
Microhabitat often differs between nest trees and non-nest trees of cavity-nesting
species (Li and Martin 1991, Lundquist and Mariani 1991, Adkins-Giese and Cuthbert 2003).
Snags were more likely to be used as nest-sites by Red-breasted Nuthatches as cavity-cover
decreased (Table 3.8). Although dense vegetation is important in avoiding nest predation for
cup nesters, cavity nesters rely more on nest defense than on nest concealment (Martin 1992).
Failed nests tended to have more canopy cover (Li and Martin 1991). Therefore, cavity
nesters may prefer nest sites that are more open and less concealed by vegetation (BellesIsles and Pieman 1986, Finch 1989, Li and Martin 1991, Lawler 1999). Cavity-nesters often
choose nest-sites among clusters of snags rather than snags surrounded by live trees
(Swallow et al. 1986, Lundquist and Mariani 1991, Martin 1998). The association between
the number of snags around potential nest trees and nest placement was significant at Hungry
Bob for Red-breasted Nuthatches as well (Table 3.8). Trees with larger diameters were more
likely to be used as nest-sites by Pygmy Nuthatches (Fig. 3.8). Preference by cavity-nesting
birds for large diameter snags has been extensively documented, and has been proposed to be

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due to a greater proportion of sapwood which is softer for excavation as well as increased
wall thickness which makes predator entry more difficult (Bull et al. 1997).
There was no difference in daily nest survival or nest density to support the
hypothesis that habitat quality differed for Red-breasted Nuthatches between restorative
treatment units and control units. However, ‘thin and bum ’ units had the least amount of
snags (Table 3.6). Density of Red-breasted Nuthatch nests has been correlated with snag
density in other studies (Swallow et al. 1986, Steeger and Hitchcock 1998). There may have
been a preference for ‘thin and bum’ treatments that was masked by limited nest-sites.
Comparison of fecundity of nuthatch nests among treatment types may have shown
differences in habitat quality that were more subtle than binary measures of nest success.
Pygmy Nuthatches are excellent indicators of ecosystem health within ponderosa pine
owing to their preference for mature, heterogeneous, and open stands (Diem and Zeveloff
1980, Szaro and Baida 1982). The Pygmy Nuthatch is classified as a sensitive species within
the Blue Mountains of Oregon and is listed on conservation watch lists in Colorado,
Montana, and Wyoming because of habitat loss (Webb 1985, Clark et al. 1989, Luce et al.
1997, US Fish and Wildlife Service 2002, Idaho Bureau of Land Management 2003). As a
result, Wisdom et al. (2000) recommended restoration within ponderosa pine habitats after a
thorough analysis of the effects of treatments upon Pygmy Nuthatches. Habitat quality for
Pygmy Nuthatches may be increased by a combination of restorative thinning and burning
within ponderosa pine ecosystems. Thinning alone may be detrimental to the species.
Pygmy Nuthatches were less common within Hungry Bob than Red-breasted Nuthatches.
For this reason, a larger study area or more years of research are needed in order to compare

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daily nest survival among treatment types. This could reveal the reasons behind decreased
nesting density within the ‘thin’ treatment units.

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4. General Discussion
4.1. The Effects of Restorative Treatments within Ponderosa Pine on Nuthatches
Pygmy Nuthatches (Sitta pygmaea) appear on state conservation watch lists across
the western United States (Webb 1985, Clark et al. 1989, Luce et al. 1997, US Fish and
Wildlife Service 2002, Idaho Bureau of Land Management 2003). Silvicultural and burning
treatments that restore ponderosa pine (Pinus ponderosa) as the dominant tree species need
to be evaluated as part of a conservation effort for Pygmy Nuthatches as well as other birds
closely associated with ponderosa pine habitats, such as the White-headed Woodpecker
(Picoides albolarvatus; Wisdom et al. 2000). Pygmy Nuthatches and White-breasted
Nuthatches (S. carolinensis) were encountered least frequently in ‘thin’ units and ‘control’
units, respectively. Sample size of nests for both species of nuthatch were too small to
determine statistically whether nest density followed the same pattern. Pygmy Nuthatches,
however, had no nests in ‘thin’ units. The preference of Pygmy Nuthatches for open stands
(Baida et al. 1983, Csuti et al. 1997, Kingery and Ghalambor 2001) cannot explain their
absence in ‘thin’ units. Both ‘control’ and ‘bum’ areas had a similar or greater amount of
canopy closure (Table 2.18). A strong preference for large diameter trees was exhibited by
Pygmy Nuthatches by both their foraging and nesting behavior (Figs 2.5 and 3.8). The
largest trees were found in ‘bum ’ and ‘thin and bum’ treatment units (Fig. 2.18).
The encounter rate and nest density of Red-breasted Nuthatches {S. canadensis) was
consistent among treatments. There were fewer snags within ‘thin and bum’ units. Most
cavity-nesting bird densities are positively correlated with the number of snags within an
area, especially when snags are limiting (Hejl et al. 1995, Beese and Bryant 1999, Chambers
et al. 1999, and Machmer 2002). Nest-sites may be limiting within this area of the Blue

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Mountains (Rothenbach and Opio 2005), so the reduced snag numbers within the ‘thin and
bum ’ explains the reduced Red-breasted Nuthatch nest density. Red-breasted Nuthatches
spent significantly more time on each tree in ‘thin and bum ’ units than any other unit,
indicating that food may be more abundant or desirable within stands treated with thinning
and burning (Morrison et al. 1989).
None of the species spent a different proportion of their time actively foraging
between treatments. This result is hard to interpret because nuthatches are known to cache
their food, and cache far more than they eat in one day (Grubb and Waite 1987). Food might
not have been limiting within this system, as has been shown for other ponderosa pine forests
(Brawn et al. 1987). If this is the case, nuthatches may allocate a consistent proportion of
their time in foraging, and cache any extra food that is captured during the day.
Pygmy Nuthatches serve as excellent indicators of ecosystem health within ponderosa
pine owing to their near exclusive residence within mature, heterogeneous, and open stands
(Diem and Zeveloff 1980, Szaro and Baida 1982). Thinning and burning, when applied
together, seem to increase habitat quality for nuthatches. Burning and thinning, when applied
separately, seem to alter habitat little for White-breasted and Red-breasted Nuthatches, and
may decrease habitat quality for Pygmy Nuthatches. In light of the results of this research,
restorative treatments that use a combination of thinning and burning may be beneficial to
Pygmy and White-breasted Nuthatches.
4.2. Future Research
The behaviors of foraging birds vary across time within ponderosa pine ecosystems
(Hejl and Vemer 1990, Szaro et al. 1990), among stages of the nesting cycle (Sakai and
Noon 1990), and even among birds within differing social structures and dominance

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hierarchies (Grubb and Woodrey 1990, Hanowski and Niemi 1990). The research reported
in this thesis was not designed to take into account these variations. Models with greater
complexity than those presented here may capture more of the error inherent in the
assumptions of each model taken separately. For example, density estimates alone without a
measure of individual reproductive success or survivorship fails to differentiate high quality
territories from ecological sinks that are attractive to low-quality or first-year breeding pairs
(Smallwood 2001).
There were many facets undertaken at the beginning of this research that could have
added to the interpretation of the results, but were not pursued further because of financial
and time constraints. For example, the analysis of nest density could have been augmented
by an analysis of territory size. Nest density can be a comparative measure of territory size,
so long as birds are located consistently across the landscape (Krebs 1971). This was not the
case with Pygmy and White-breasted Nuthatches. A direct measurement of territory size can
be an excellent indication of habitat quality, especially when combined with foraging
analyses (Brooker and Rowley 1995). This would have to be accomplished with a longer
term study so that a population of birds could be banded during the winter months. Mistnetting using call-playback methods had a very low rate of success during the breeding
season. Also, fecundity measurements could have added the ability to differentiate between
source and sink areas in Hungry Bob (Brawn and Robinson 1996). A peeper camera was
purchased in order to compare fecundity between treatments, but it was unsuccessful, so
other methods would have to be used to obtain those data in future studies.

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