Vocal deviation and trill consistency do not affect male response to playback in house wrens

Abstract

Signals that require a high degree of skill to produce are expected to honestly indicate signaler quality. In trilled birdsong, 2 parameters that likely reflect performance difficulty are vocal deviation (how rapidly sound frequency is modulated) and trill consistency (how precisely syllables are repeated). These parameters function as intra- and intersexual signals in most bird species tested to date, but they may not adequately capture song performance difficulty in all species. I used 2 playback protocols to test whether males respond differently to songs that differ in vocal deviation and trill consistency in house wrens (Troglodytes aedon). Despite large sample sizes, male responses did not depend on playback treatment. Males sang each trill type at a range of pitches, and the vocal deviation of the trill depended strongly on the pitch at which it was sung, consistent with models of song production mechanics. I propose that the addition of the pitch covariate may complicate the evaluation of vocal deviation, limiting the usefulness of this potential signal for this species. Moreover, producing each trill type at a range of pitches may itself serve some communication function, which could override the potential signal value of trill consistency. Although vocal deviation and trill consistency are male quality indicators in some species, these results suggest that species-specific differences in what constitutes a challenging song may prevent these measures from being universally applicable.