1926] Swarth: Birds and Mammals from the Atlin Region 81

of all the forms of Dendragapus there is more or less variation with
age in the shape of the tail feathers, in the length of the tail, and in
the shape of the tail as a whole.

In the plumage as a whole there is marked seasonal variation, too,
that must be taken into account. Birds in fresh fall plumage (both
sexes and both the yearlings and fully mature) are of a clearer blue-
gray, compared with late spring and summer specimens, in which this
color has changed to a dingy brown.

Fig. E. Tails of Dendragapus fuliginosus sitkensis, showing variation due to
sex and age, about % natural size. a, adult male, in second year or older (M.V.
Z. no. 133) ; b, immature male, during first year (M.V. Z. no. 136); c, adult female
(M.V.Z. no. 134); d, immature female (M.V.Z. no. 135).

Relative roundness of tail, besides being a marked age character in
certain forms, is also a feature in geographical variation. The sub-
species howardi was described as having the tail longer and more
graduated than sierrae (Dickey and van Rossem, 1923, p. 168), and
the comment is made that ‘‘throughout the range of Dendragapus
obscurus in California there is a gradual geographic variation which
particularly affects the length and graduation of the tail.’’ This same
variation can be traced beyond California. From the northern limit