Female Song Occurs in Songbirds with More Elaborate Female Coloration and Reduced Sexual Dichromatism

Abstract

Elaborate plumages and songs in male birds provide classic evidence for Darwinian sexual selection. However, trait elaboration in birds is not gender-restricted: female song has recently been revealed as a taxonomically-widespread trait within the songbirds (oscine Passerines), prompting increased research into likely functions and social/ecological correlates. Here we use phylogenetically-informed comparative analysis to test for an evolutionary association between female song and plumage color elaboration in songbirds. If there is an evolutionary trade-off between signaling modes, we predict a negative correlation between acoustic and visual elaboration. This trade-off hypothesis has been commonly proposed in males but has mixed empirical support. Alternatively, if song and plumage have similar or overlapping functions and evolve under similar selection pressures, we predict a positive correlation between female song and female plumage elaboration. We use published data on female song for 1023 species of songbirds and a novel approach that allows for the reliable and objective comparison of color elaboration between species and genders. Our results reveal a significant positive correlation between female colorfulness and female song presence. In species where females sing, females (but not males) are on average more colorful-with concomitantly reduced average sexual dichromatism. These results suggest that female plumage and female song likely evolved together under similar selection pressures and that their respective functions are reinforcing. We discuss the potential roles of sexual vs. social selection in driving this relationship, and the implications for future research on female signals.

Is sexual dimorphism in singing behavior related to syringeal muscle composition?

“…Most females possess complex call repertoires; the female Streak-backed Oriole (Icterus pustulatus) sings more than the male (Price et al 2008). In addition, female traits (e.g., singing) can evolve rapidly and independently (Webb et al 2016) and be under weakened selective pressure. One idea may be that weak selection may cause more variable content of superfast fibers in females across different species.…”

Song function and territoriality in male and female White-throated Dippers Cinclus cinclus

“…Once thought to be rare, female song is now known to be widespread and evidence suggests that it is ancestral (Odom et al 2014). It is most prevalent in non-migratory species with year-round territoriality (Price et al 2008, Tobias et al 2016, and is closely associated with monogamy and sexual monochromatism (Najar & Benedict 2015, Webb et al 2016. However, studies of the function of song in females are largely restricted to duetting species (Hall & Peters 2008, Logue & Krupp 2016 and those that live in the tropics and Australasia (Slater & Mann 2004, Brunton & Li 2006, Odom & Benedict 2018.…”

Evolution of a mating preference for a dual‐utility trait used in intrasexual competition in genetically monogamous populations

“…Intrasexual resource competition offers a mechanism by which a link between an ornamental trait and fecundity could emerge: if ornamented females, for example, are more likely to win competitions with other females for access to resources that enhance fecundity, such as high-quality territories or food resources, males that prefer ornamented females will have more fecund mates (Tobias, Montgomerie, & Lyon, 2012). Emerging evidence supports the idea that, as suggested by multiple reviews covering the function and evolution of female ornamentation Tobias et al, 2012;Webb et al, 2016;West-Eberhard, 1983), female visual and vocal ornaments are often used in female-female competition over resources related to reproductive success Cain et al, 2015;Crowhurst, Zanollo, Griggio, Robertson, & Kleindorfer, 2012;Kraaijeveld et al, 2004;Krieg & Getty, 2016;Murphy et al, 2009a,b;Pryke, 2007;Stankowich & Caro, 2009;Watson & Simmons, 2010). For example, female black swans (Cygnus atratus) with more curled feathers are more likely to win female-female agonistic interactions, and number of curled feathers also predicts the ability to maintain territory ownership, which leads to higher offspring survivorship (Kraaijeveld et al, 2004).…”