Animals exhibit a diverse array of elaborate traits, from flashy colors to the complex songs of songbirds. Such elaborate traits are classically thought to evolve predominantly in males through sexual selection. A prime example is bird song: male songs appear to have been selected to become more elaborate to attract females or compete with rival males, whereas females were thought primarily to listen and choose a mate. Research we published in 2014 showed that female song is surprisingly common and most likely was ancestral in songbirds. Thus, the diversity of bird song we see today must be due, in part, to female song becoming reduced or lost during the course of evolution in some lineages. Our current research aims to (1) document how female and male songs have changed through evolutionary time, and (2) to identify what factors have led to elaboration of song in both sexes in some lineages, but losses of female song in others.

A tree full of songs

The structure of female and male song varies widely among species. To quantify this variation, we are collecting songs from researchers, biological collections, and sound libraries around the world. We will measure fine details of female and male songs using standardised metrics. which we can then map onto a phylogenetic tree of relationships among bird species. Using ancestral state reconstruction, we will then reconstruct how female and male song has changed over time.

Making her voice heard!

Because bird song research previously focused on male songs, female bird song is underrepresented in biological collections. To understand bird song evolution in both sexes, we need recordings of female bird songs for large numbers of species. To address the lack of female bird song recordings, we are launching a citizen science project to increase awareness and encourage documentation of female bird song. We are working together with Cornell’s Macaulay Library of Natural Sounds and Xeno-canto, the largest online database of bird songs, sponsored by Naturalis Biodiversity Center. We want to encourage citizen scientists, birders, and wildlife recordists to submit observations and recordings of female bird song to biological collections. We are in the process of creating a project website with information on how to contribute. Stay tuned as these materials become available.

• development & disease
• evolution & biodiversity

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