Effect of habitat quality on communication and signalling in the black-capped chickadee.

Vocal performance in songbirds describes the ability to repetitively perform energetically-expensive acts (vocal vigour) and/or to consistently perform difficult motor tasks (vocal skill). This concept is intrinsically correlated with the birds' condition - birds in better condition tend to signal with higher performance than birds in poorer condition (e.g. vocal performance is condition-dependent). Condition of birds, however, is also influenced by the habitat quality in which they settle, and has been well studied in the black-capped chickadee. My Ph.D thesis explores the links between habitat quality and vocal performance in this species. Previous studies have shown that habitat quality affects song output in this species (reduced vocal vigour in poor-quality habitat) and it was speculated that reduced song output may be linked to poorer condition of birds in these forests. To document the relationship between immediate food availability and vocal performance, I conducted a supplemental feeding experiment on male chickadees during the peak in dawn singing in early spring. My results demonstrate that food availability is an important factor influencing song output, and that song output reflects the condition of the birds at the time of singing. The difference in song output across habitats, thus, appears to relate to difference in food availability at the time of singing. The ability to maintain internal song structure (vocal skill) has previously been shown to be condition-dependent in chickadees, with dominant birds having better vocal skill than subordinate birds. My supplemental feeding study demonstrated that this vocal skill is not influenced by short-term resource availability to the signaller at the time of singing, but vocal skill is affected by habitat quality - birds in young forest habitats (poor-quality) are less able to maintain internal frequency ratios in their songs than birds in neighbouring mature forests (high-quality). The ability to maintain internal song ratios may rather reflect longer