Until recently, researchers thought that most of the birds that sing were males. But in 2016, Karan Odom went through samples of songs from more than a thousand species from around the world and found that 64 percent of the species had females that sing.
Odom is a Postdoctoral Research Fellow at Leiden University and the Cornell Lab of Ornithology. She has launched a new citizen science initiative called the Female Bird Song Project.
Why do we assume that females don't sing as much as males? It has to do with where the most intense study of birds got started—in temperate locations, where birds are more migratory. In those areas, males sing to attract females, and females sing less, probably to avoid predation on the nest. But in tropical locations, both male and female sing a lot.
"If you go to the tropics, a lot of birds are staying in the same place. They have a territory," said Odom.
To defend their territory and resources, it may require defense by the male and female. So, the female and male have more similar roles.
Take the male troupials in Puerto Rico, for instance. Odom said she heard males singing at dawn and they seem to sing where they were guarding or protecting female. With the female troupial, though, there was no difference in the kinds of songs. The females can sing equally complex songs as the males.
"Sometimes they sing together in a duet," Odom said. "It's a joint territory defense."
It's a strategy that seems to work as a strong signal to tell other birds to stay off of their territory and away from their resources.
But it’s not only tropical birds. Take your ordinary backyard cardinal. It’s difficult to hear the differences between the male and female song, but both sexes do sing. Take a closer look the next time you hear a cardinal. It might be a female.
Odom is asking birders from around the world to take part in the Female Bird Song Project.
First, be aware that any bird you hear could be a male or a female. Then, get a good look at the bird you hear and determine the sex. Finally, make an audio recording and send it in to the project.
More information regarding how to participate can be found on their website.