Vocal performance influences female response to male bird song: an experimental test

Abstract

Female songbirds are thought to assess males based on aspects of song, such as repertoire size or amount of singing, that could potentially provide information about male quality. A relatively unexplored aspect of song that also might serve as an assessment signal is a male's ability to perform physically challenging songs. Trilled songs, such as those produced by swamp sparrows (Melospiza georgiana), present males with a performance challenge because trills require rapid and precise coordination of vocal tract movements, resulting in a trade-off between trill rate and frequency bandwidth. This trade-off defines a constraint on song production observed as a triangular distribution in acoustic space of trill rate by frequency bandwidth, with an upper boundary that represents a performance limit. Given this background on song production constraints, we are able to identify a priori which songs are performed with a higher degree of proficiency and, thus, which songs should be more attractive to females. We determined the performance limit for a population of swamp sparrows and measured how well individual males performed songs relative to this limit (''vocal performance''). We then compared female solicitation responses to high-performance versus lowperformance versions of the same song type produced by different males. Females displayed significantly more to highperformance songs than to low-performance songs, supporting the hypothesis that females use vocal performance to assess males.

The ability to perform physically challenging songs predicts age and size in male swamp sparrows, Melospiza georgiana

“…Thus, males with superior vocal performance are likely to positively influence female reproductive success directly and/or indirectly. This is the first study showing that female preference for vocal performance (Ballentine et al 2004) in males may be an adaptive female choice for a reliable signal of male quality.…”

“…Together these studies suggest that female preferences for trilled portions of songs in canaries might be driven by female preferences for portions of songs that are difficult to produce. In a laboratory experiment, female swamp sparrows gave more copulation solicitation postures to natural songs that were closer to the performance limit (Ballentine et al 2004). This empirical evidence of female preferences for physically challenging songs supports the general hypothesis that vocal performance is a reliable signal of male quality, but it does not rule out alternative hypotheses such as sensory biases (Ryan et al 1990) or runaway selection (Fisher 1930).…”

“…Songs were recorded using a Sony TCD-5000 EV recorder with either a Shure SM-57 microphone and a Sony Parabolic Reflector-330 or a Saul Mineroff SME Parabolic Reflector-1000. The same recording equipment was used throughout this study, and thus, differences between individuals or between years in acoustic features of song were not due to differences in equipment, and when used in previous studies, this equipment resulted in highly repeatable acoustic measurements (Ballentine et al 2004).…”

“…The method for quantifying vocal performance is described in detail elsewhere (Podos 2001;Ballentine et al 2004;Ballentine 2006a). Briefly, I plotted trill rate (X axis) and frequency bandwidth (Y axis) of songs, then calculated an upper boundary regression, which estimates the performance limit on trill production (Podos 2001).…”

Female mate choice based upon male motor performance

“…For example, female canaries, Serinus canaria (Draganoiu et al 2002) and swamp sparrows (Ballentine et al 2004) prefer (laboratory copulation solicitation display tests) trills that are close to mechanical performance limits; male chestnut-sided warblers, Dendroica pensylvanica, that sing high-frequency notes with greater consistency attract more extrapair mates (Byers 2007); male chickadees, Poecile atricapillus, with the most consistent internote ratios are most dominant at feeders (Christie et al 2004); male blue tits, Cyanistes caeruleus, with highly consistent intersong intervals tend to sire more offspring (Poesel et al 2001); and territorial male nightingales, Luscinia megarhynchos, are repelled more effectively by playback of song bouts that include higher proportions of trilled songs (Schmidt et al 2008). In satin bowerbirds, Ptilonorhynchus violaceus, male attractiveness to females is strongly correlated with the number of other species' songs that the male mimics, and with the accuracy of the mimetic copies (Coleman et al 2007).…”