Female Lincoln's sparrows modulate their behavior in response to variation in male song quality

Abstract

Sexually reproducing organisms should mate with the highest quality individuals that they can. When female songbirds choose a mate, they are thought to use several aspects of male song that reflect his quality. Under resource-limited environmental conditions, male Lincoln's sparrows (Melospiza lincolnii) vary among one another in several aspects of song quality, including song length, song complexity, and trill performance. In a 2-pronged approach, we tested whether variation in song quality of male Lincoln's sparrows influences the behavior of females that are in a reproductive-like state. Over two trials, we exposed females to songs from the high and low ends of the distribution of naturally occurring song quality variation and found a higher level of behavioral activity in females exposed to high-quality songs, especially when they had first been exposed to low-quality songs. We also examined female phonotaxis toward antiphonally played songs with experimentally elevated and reduced trill performance and found that females moved preferentially toward the songs with elevated trill performance. Contrary to most studies investigating the behavioral responses of wild, female songbirds to variation in male song, we obtained our results without administering exogenous estradiol, which can artificially perturb the female's physiology. Our results demonstrate that the behavior of female Lincoln's sparrows is modulated by the quality of male songs to which they are exposed and that trill performance plays a significant role in this behavioral modulation. Furthermore, as the order of song quality presentation matters, it appears that recent song experience also influences female behavior.

Avian ecologists and physiologists have different sexual preferences

“…The major drawback of hormone implants is that they alter the normal physiology of the female by creating an artificial hormonal environment [15,23], and this restricts the array of applications. GnRH injections however do not induce supra-physiological levels of hormones because they only release the amount of hormone that is stored in the endocrine glands in a similar fashion as a social stimulus would do [16,51,75].…”

Contrast influences female attraction to performance-based sexual signals in a songbird

“…To determine the direction of the effect, one would need also to expose females to intermediate-performance versions of the treatment songs to control for overall attractiveness of the novel songs. However, we had no such control nor any pre-conceived expectations of the overall attractiveness of the novel, intermediate-performance songs, as Lincoln's sparrows' songs vary in many aspects other than performance, and these aspects can also influence songs' attractiveness [13]. Instead, we predicted only that intermediate-performance song would be more attractive after exposure to low-performance songs than after exposure to high-performance songs.…”

“…In July 2010, we collected 8-day-old Lincoln's sparrow chicks near Molas Pass, CO, USA (37.748 N, 107.698 W) and reared them in outdoor aviaries at the University of North Carolina (Chapel Hill, NC, USA) [13,15]. Starting March 2012, we moved 12 females indoors into individual cages on a 16 L : 8 D photoperiod for 21 days to drive them into a reproductive-like state [16].…”

“…We quantified the time females spent in the half of the cage nearest the active speaker for 3 min before (baseline) and the first 3 min during (phonotaxis) song exposure [13,15].…”

“…Owing to a biomechanical constraint of the vocal tract, the performance of trilled syllables in the songs of many songbird species reflects a trade-off between maximizing the rate of syllable repetition and maximizing the frequency bandwidth of those syllables [9,11]. Trill performance varies within and between males [11,12], and in several species females prefer high-performance trills in mate-choice contexts [9,13]. In Lincoln's sparrows (Melospiza lincolnii ), females prefer songs with high-performance trills [13], and there is annual variation in a population's mean level of trill performance [12].…”