Analysis of female song provides insight into the evolution of sex differences in a widely studied songbird

Abstract

Understanding the patterns and processes related to sexual dimorphism and sex differences in diverse animal taxa is a foundational research topic in ecology and evolution. Within the realm of animal communication, studies have traditionally focused on male signals, assuming that female choice and male-male competition have promoted sex differences via elaboration of male traits, but selection on females also has the potential to drive sexual differentiation in signals. Here, we describe female song in barn swallows (Hirundo rustica erythrogaster) for the first time, report rates of female song production, and couple song data with plumage data to explore the relative degree to which sex differences in phenotypic traits are consistent with contemporary selection on males versus females. During previous intensive study of male song over two years, we opportunistically recorded songs for 15 females, with matched phenotypic and fitness data. We randomly selected 15 high-quality samples from our larger male dataset to test whether sex differences in song and plumage are more strongly associated with fledgling success for females or genetic paternity for males. Analyses included 35 potential sexual signals including 22 song parameters and 13 plumage traits. Outcomes indicate that: female songs were used in multiple contexts, restricted primarily to the beginning of the breeding season; song traits showed greater sexual differentiation than visual plumage traits; and trait correlations with reproductive success in females, rather than males, predicted sex-based differences in song and plumage. These results are consistent with phylogenetic studies showing that sex-based phenotypic differences are driven by changes in females, highlighting the potential role of female trait evolution in explaining patterns of sexual differentiation. To achieve a better understanding of sex differences and dimorphism, we require comprehensive studies that measure the same traits in males and females and their fitness consequences.

Sexual and temporal variation in New Zealand bellbird song repertoires

“…The two song types that female red-winged blackbirds sing are different in structure compared to male song (Beletsky, 1983; Catchpole and Slater, 2008), but there is no detail on what syllable types they may share. Some species have similar syllable structure between the sexes but have differences in the overall or particular spectral parameters of their song (Dutour and Ridley, 2020; Hahn et al, 2013; Wilkins et al, 2020; Yamaguchi, 1998). For example, northern cardinal ( Cardinalis cardinalis ) female song has been described as a neotenic version of male song, but it also differs from males in the amplitude of harmonics and syllable stereotypy (Yamaguchi, 1998).…”

La voz de nuestras aves: contribuciones de la bioacústica a la ornitología colombiana

“…4.2 Escuchándolas en Colombia.-Concretamente, en el Neotrópico el conocimiento sobre la prevalencia del canto en las hembras está pobremente documentado, a pesar de que se conoce que las hembras no sólo producen cantos facultativos, sino que también pueden realizar exhibiciones acústicas junto con los machos para formar duetos vocales (Logue & Gammon 2004, Hall 2009, Templeton et al 2013, Odom et al 2017, Hathcock & Benedict 2018. En la zona tropical, el canto de las hembras se ha descrito como menos complejo o frecuente que el de los machos (e.g., Hypocnemis peruviana e H. subflava; Tobias et al 2011; Hirundo rustica erythrogaster, Wilkins et al 2020), pero se destacan algunas investigaciones en especies tropicales en donde se describe que las hembras, i) cantan con más frecuencia que los machos, pero sus parámetros acústicos se superponen entre los sexos (e.g., Icterus pustulatus; Price et al 2008 Seeholzer & Gamarra 2020). Particularmente, en aquellas especies en donde machos y hembras lucen plumajes casi iguales, se ha llegado a asumir que todos los cantos son producidos por los machos, limitando el análisis de los patrones evolutivos en la variación vocal de las aves (Price et al 2008, Price 2015, Derryberry et al 2018.…”

“…Estas condiciones han resultado en que, por décadas, el estudio del comportamiento vocal en hembras se haya descuidado. Afortunadamente, esta tendencia está cambiando en los últimos años, demostrando que las hembras pueden exhibir comportamientos complejos asociados al uso de vocalizaciones (Ficken et al 2002, Riebel 2003, Wilkins et al 2020. A pesar de que las habilidades vocales de las hembras no han sido estudiadas ampliamente, sus preferencias por ciertos cantos o características acústicas específicas han recibido mayor atención, ya que estas preferencias tienen implicaciones evolutivas en el contexto de selección sexual y éxito reproductivo (Nowicki & Searcy 2004), por ejemplo, la preferencia por cantos locales versus cantos foráneos.…”

Female song is structurally different from male song in Orchard Orioles, a temperate-breeding songbird with delayed plumage maturation

“…However, recent studies examining selection pressures in songbirds have suggested that greater variability in female songs may be selected for if female vocal signals are more limited in diversity and duration (Collins et al 2009, Wilkins et al 2020).…”