Rethinking our assumptions about the evolution of bird song and other sexually dimorphic signals

Abstract

Bird song is often cited as a classic example of a sexually-selected ornament, in part because historically it has been considered a primarily male trait. Recent evidence that females also sing in many songbird species and that sexual dimorphism in song is often the result of losses in females rather than gains in males therefore appears to challenge our understanding of the evolution of bird song through sexual selection. Here I propose that these new findings do not necessarily contradict previous research, but rather they disagree with some of our assumptions about the evolution of sexual dimorphisms in general and female song in particular. These include misconceptions that current patterns of elaboration and diversity in each sex reflect past rates of change and that levels of sexual dimorphism necessarily reflect levels of sexual selection. Using New World blackbirds (Icteridae) as an example, I critically evaluate these past assumptions in light of new phylogenetic evidence. Understanding the mechanisms underlying such sexually dimorphic traits requires a clear understanding of their evolutionary histories. Only then can we begin to ask the right questions.

The relationship between latitude, migration and the evolution of bird song complexity

“…However, this is often not explicitly tested and there is debate in the literature about how such testing should be done (Wilkins et al 2013, Byers 2015, Price 2015. None of the studies included here measured proxies of sexual selection, such as time to pairing, reproductive success, or level of parasite or disease infection, leaving room for improvement in future studies.…”

Audition and Hemispheric Specialization in Songbirds and New Evidence from Australian Magpies

“…This correlation, so they show, accounts for almost half of the observed variation in telencephalic size, more than any other behavioral specialization examined, including the ability to learn song. Moreover, female song is widespread and ancestral in birds [38][39][40][41]. In other words, as was recognized some time ago, relying on the zebra finch model in terms of broader questions of behavior could lead to ignoring the importance of social learning in non-reproductive contexts [42,43], the significance of variability in avian communication outside the breeding context and the possibility of different underlying mechanisms of brain activity [44][45][46] for hearing and vocal production, of which lateralization may be an important manifestation.…”

Superb Fairy-Wren (Malurus cyaneus) Sons and Daughters Acquire Song Elements of Mothers and Social Fathers

“…There is growing evidence that female song is "common" rather than "exceptional" (Riebel et al, 2005;Garamszegi et al, 2007;Price, 2009;Odom et al, 2014), which focuses research attention on the role of sexual selection for complex female song (Price, 2015). Song complexity in females varies greatly across species (Odom et al, 2014;Price, 2015).…”

“…There is growing evidence that female song is "common" rather than "exceptional" (Riebel et al, 2005;Garamszegi et al, 2007;Price, 2009;Odom et al, 2014), which focuses research attention on the role of sexual selection for complex female song (Price, 2015). Song complexity in females varies greatly across species (Odom et al, 2014;Price, 2015). As discussed by Price (2015): "Although female song is often treated as a discrete binary character in comparisons among species, with some species categorized as having female song and others not (e.g., Garamszegi et al, 2007;Price, 2009;Odom et al, 2014), evidence suggests that female singing can vary continuously across taxa in both expression and complexity."…”

“…Song complexity in females varies greatly across species (Odom et al, 2014;Price, 2015). As discussed by Price (2015): "Although female song is often treated as a discrete binary character in comparisons among species, with some species categorized as having female song and others not (e.g., Garamszegi et al, 2007;Price, 2009;Odom et al, 2014), evidence suggests that female singing can vary continuously across taxa in both expression and complexity." To date, we know very little about how this complexity in female song arises.…”