Female birds sing. This is one of the conclusions of our study 2020 on one of the most abundant, widespread, and best-studied bird species in the world: the barn swallow. Despite more than 1,000 scientific publications on this species, the song of the barn swallow has never been the subject of a research article before.
Why is it important that female song was ignored in this bird that breeds across most of North America? It highlights a long-standing scientific bias and helps us think about why this bias persists.
Since the beginning of modern bird song research, the field has focused on the conspicuous songs of male songbirds. Conventional evolutionary theory assumes that throughout the animal kingdom, males compete for access to females, causing male animals to develop exaggerated traits (like antlers) that help them fight off other males, as well as features (like the fabulous peacock feathers) that attract females. Birdsongs can work in both of these contexts, and although males may have more elaborate songs than females, this is far from universal. In fact, females sing in at least 64% of songbird species, and their songs can serve the same functions as the songs of males.
Yet many researchers still assume that “the male bird sings and the female chooses”, with field studies largely focusing on the most abundant male cues. The most frequent song, however, may not always be the most important, just as a debate can be settled by who had the last word rather than who spoke the most. Our study suggests that the evolution of female barn swallow songs is more important than the evolution of male songs in explaining why the two sexes sound different.
A second reason for the neglect of female bird song stems from geographical bias. Any serious ornithologist or ornithologist working in the tropics could tell you that females sing, sometimes as often as males. But early researchers tended to study species near their universities in the northern hemisphere. In a large proportion of North American birds, females have lost or reduced their songs, which may represent evolutionary adaptations to conserve energy for migration or to focus on breeding for a short season.
A final reason why female bird song is understudied could be sex. Humans have dominated bird song research since its inception. However, as more and more women entered the field, they stimulated an exuberant surge in the study of women’s song. The women are much more likely than males to be first authors of female bird song articles. The historical lack of diverse participation in science may have contributed to researchers forming self-reinforcing assumptions that have hindered a full understanding of the world around us.
To combat these biases in the scientific canon, we need to make science more accessible to everyone. For example, if we can make people aware that female birds sing, we will improve their experience of nature and improve their ability to observe it. In many species, including barn swallows, males and females look alike from a distance but can be distinguished by ear. Female barn swallows mainly sing just before they start breeding, knowing that this can help observers track the timing of barn swallow nesting, for example. Initiatives such as xeno canto and eBird collect millions of public sightings and audio recordings of birds each year. People who understand the latest scientific advances will create better global datasets, which in turn will generate better science.
Non-scientists make better observers because they lack preconceived notions. One of us (Benedict) often speaks to public groups and finds that birders (“experts”) tend to assume that female birds don’t sing, while non-birders tend to assume that birds females can sing. The lessons on authentic science are ideal for engaging children, in particular, who have not yet absorbed existing prejudices. One of us (Wilkins) adapted our research on female songbirds into a interdisciplinary lesson for students in grades 5-12 (available at galacticpolymath.com). Wilkins once told a fifth-grade math class that they were among the first in the world to explore a data set. from a study of how the vocal pitch of birds decreases with body sizeand they spontaneously clapped.
Female birds sing! We must state this truth so emphatically because it reflects the constant adjustments of scientific consensus as new facts become available and new voices are added to the conversation. We welcome a future where research, communication and education combine to deepen our connections with each other and with the natural world.