Female birds often get short shrift. Sometimes smaller and less flamboyantly hued than their male counterparts, they’re often imagined to be quieter, too.
Sex-specific song information only exists for about a quarter of all songbird species—but of those species in which males are known to sing, 64 percent also have female singers. In some species, female song might be a little less complex or weaker than male versions, but can also be quite the opposite: Some female owls, for instance, have longer, more emphatic calls, or use more notes.
Even if female song is pretty pervasive, documentation is scant. That’s partly due to what Karan Odom, a researcher at the Cornell Lab of Ornithology, dubs a “temperate bias.” Historically, a lot of research into bird song has been concentrated in temperate regions, where male song predominates—instead of in more tropical zones, where there’s more parity. (Out of the 660 known species with female singers, only 18 percent are found in the continental U.S., Hawaii, or Canada, Audubon noted.)
Even when researchers have listened for female songs in the tropics, it can be difficult to tell the singer’s sex from a distance: Both males and females often wear blazing hues and bold ornamentation. “In the majority of species, unless I knew that bird really well, I couldn’t tell just by listening,” says Odom. Banding birds with sex-specific bracelets can help researchers distinguish between them. In species for which researchers know that incubating and nest-fluffing are the exclusive domains of females, those behaviors can also offer clues about who is making all that noise.
Odom argues that there’s much to be gleaned by listening in to female song, whether that happens to be in the tropics or by craning an ear to the Northern Cardinal perched in a tree outside my New York City window. That was the thrust of a commentary that Odom and her collaborator Lauryn Benedict of the University of Northern Colorado recently published in The Auk: Ornithological Advances, calling on other researchers—and citizen scientists—to keep an eye and ear out for female birds and their songs. Odom has turned to troves of recordings collected over the span of decades, such as those in the wildlife-focused Macaulay Library. Paired with field notes, these snippets offer valuable information about who is singing, and where. Contributors can also upload sound clips and field observations to the Female Bird Song project, which Odom manages with partners at Leiden University in the Netherlands.
By examining species where females sing, Odom says, researchers can probe all sorts of evolutionary, ecological, and neurobiological questions. Song is a complex, learned behavior. At what point in their lives do females learn their song? Then, where and when do the female birds belt their little hearts out?
In male species, Odom says, complex songs are often thought of as being tied to sexual selection, indicating that a bird might make a good mate or a ferocious defender of territory. “So then the question is why do females songs become complex?” The reasons might be different, she says—complex female songs could indicate a bird’s ability to defend resources, or acquire food for her young. There’s plenty more to learn, Odom says. “Males are only one-half of the story.”