Most of us have heard the phrase “it takes a village” when it comes to childcare. This age-old saying holds true for some songbirds, and a new study has found that this “village” has evolutionary consequences for their songs.
Birdsong is often framed as a sexually selected male trait, where male birds sing to attract a partner. However, researchers now know that female song is widespread across songbirds and is likely inherited. So, what causes females to sing, how is their song influenced by their social environment, and what does that tell us about evolution?
In a new paper published in Nature Ecology & Evolution, titled “Territoriality modulates the coevolution of cooperative breeding and female song in songbirds,” Postdoctoral Scholar Katherine (Kate) Snyder and Associate Professor of Biological Sciences Nicole Creanza, in collaboration with former Metro Nashville Public School student Aleyna Loughran-Pierce, examined how cooperative breeding, or when family members or other nonbreeding adults help parents raise their offspring, would affect the evolution of female songbirds’ ability to sing.
The team found that species with cooperative breeding are more likely to have female song, charting the evolutionary relationships of these two behaviors. Additionally, they found the species that are less territorial have a stronger association between cooperative breeding and female birdsong, suggesting that female song may be used to promote group cohesion in some species. This discovery could shed light on how human language evolved and diverged.
“Female song was only widely recognized as an evolutionarily important behavior a little over 10 years ago, and still relatively little is known about its biological consequences,” Snyder said. “Our study shows that social behavior can leave lasting evolutionary signatures on communication systems. Understanding how communication evolves in complex social systems has implications beyond birds. Vocal learning, which is exhibited by both humans and songbirds, is otherwise exceedingly rare in the animal kingdom. By studying how cooperation and territorial behavior influence communication in birds, we gain insight into how social complexity shapes evolution more generally.”
The team analyzed songbird evolutionary history across 1,041 songbird species by compiling existing data on female song, cooperative breeding, and territoriality that spans several decades, continents, and researchers, as well as the team’s own existing data on male song traits.
“The dataset that Kate has compiled has been an incredible resource for other students in our lab,” Creanza said. “She merged all of the databases of avian phenotypes, or observable characteristics, that she could find into one dataset and harmonized it with the largest available phylogeny, which is the evolutionary history and relationship of a species or group of organisms. This dataset has paved the way for nearly every rotation project and undergraduate project in my lab. To complement the dataset, Kate made a detailed codebase with an introductory walkthrough, which can help someone with no coding experience to conduct detailed evolutionary analyses of a complex behavior within a day or two.”
In this dataset, the researchers discovered a robust, bidirectional relationship between cooperative breeding and female song that can’t be explained by shared associations with territorial behavior or body size. However, territorial context does modify this relationship, with cooperative breeding and female song being common in strongly territorial species but disproportionately linked in weakly territorial lineages.
These findings suggest the potential for distinct evolutionary pathways. Female song may be maintained for resource defense in territorial species, but it may serve group coordination or social cohesion functions in cooperative, low-conflict species. Meanwhile, male song repertoire evolution slows in both cooperative lineages and lineages with familial living, suggesting that social stability imposes different selection pressures on male and female signaling.
Creanza said her lab is planning to continue studying the evolution of birdsong by investigating why some birds perform simultaneous or coordinated singing. This research, funded through a Vanderbilt Scaling Success Grant, will provide an additional perspective into how the use of birdsong for social bonding or combative purposes influences the way male and female songs evolve.
“For the most part, birds tend to avoid singing at the same time as another bird since it prevents their song from being clearly heard,” she said. “However, in some bird species, individuals—usually males—try to match or overlap their songs when in conflict with other males, such as when defending their territory. In other species, breeding pairs produce ‘duets’ when a male and female coordinate their songs by alternating in time or singing at different pitches, which can reinforce social bonds.”
Snyder said she also plans to continue research on the variations in singing behaviors and would like to dive deeper into the effects of cooperative breeding and territoriality.
“Birds are one of the most diverse and well-documented groups of animals on Earth, occupying nearly every habitat and showing enormous variation in behavior and social systems,” she said. “Birdsong is especially powerful as a model because it sits at the intersection of genetics, learning, culture, and social interaction. Songs are learned behaviors that are socially transmitted, yet they evolve across species over millions of years. That makes birds an excellent system for studying how cultural traits and biological evolution interact.”