Trill performance in a large-repertoire songbird with high song sharing, the Bachman’s sparrow

Trilled syllables in bird song are of particular interest for their potential to communicate singing ability and thus singer quality. One reason for this is that trills require high consistency of performance, specifically, minimal variation across repetitions of a learned acoustic pattern. Another is that it is challenging for birds to repeat broad-band notes rapidly. Vocal deviation (VD) is a measure of trill performance that incorporates both the repetition rate and the frequency bandwidth of syllables. Here, we test for an expected tradeoff between trill consistency and VD in Bachman’s sparrows Peucaea aestivalis, a species with individual repertoires averaging 45–50 song types and high levels of trill type sharing among individuals. We found limited evidence of a tradeoff between high consistency and low VD. To explore whether these trill performance indices might be used by listeners to compare singers, we investigate the relationships between both performance indices and song type sharing, repertoire use, and individual identity. We found that lower-VD trills were shared by more birds, that individuals sang their more consistent trill types more often, and that many pairs of males differed in performance across their shared types, with more pairs differing in trill consistency than in VD. These results are consistent with the idea that birds preferentially learn low-VD trills, subsequent success in maximizing consistency largely determines how two males compare in the overall performance of shared trill types, and in many cases, trill performance can enable comparison of male quality.