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The backyard comes alive as a male Northern cardinal belts out his exuberant, whistle-y song — but wait, how do we know the singer is a male? Unless you see an all-red bird pushing out the sounds, you really can’t be sure.

We’re losing one of the certitudes of the avian world — that it’s only males that sing — as we learn more about bird vocalizations. Surprising as it may seem, in many species females turn out melodies, just like their male counterparts. In fact, a study of recordings of 1,000 species from around the world revealed that females join the chorus in about 64% of the cases.

“Females of many other species probably also sing, but scientists don’t know about it yet because of lack of documentation,” says Karan Odom, a researcher at the Cornell Lab of Ornithology.

The female singing phenomenon is so poorly understood and so little studied that Odom has launched the Female Bird Song Project and invites us all, amateur bird-watcher and ornithologist alike, to contribute (more about this later).

A number of factors worked together to obscure the fact that females sing. For one, bird scientists believed that singing evolved only in males and was an attribute not needed by most females. For another, most studies have focused on temperate zone species, whose females sing less than those in the less-studied tropics.

We now know that in the far-back past, both genders were songsters, and a closer look at birds in North America shows at least 150 songbirds where both males and females sing.

As bird song expert Donald Kroodsma notes in his book “The Singing Life of Birds,” “female birds have been largely overlooked.”

But is this anything more than mildly interesting? Why do we need to learn more about when and why female birds sing?

Odom and her colleague Lauryn Benedict (University of Northern Colorado) argue that singing is a complex behavior and we need to take both genders into account to truly understand it.

One example: When agencies and organizations focus on birds whose populations are dwindling, they need surveys to get a good start count. Field workers listening for songs to locate and identify birds traditionally count singers as males. However, some may actually be females, skewing the study and perhaps misleading wildlife managers. A better understanding of which female birds sing and when and why they do so will advance our understanding of birds, Odom says.

Many of us are eager to participate in citizen science projects and the Female Bird Song Project sounds like a good one. To get started, visit the website femalebirdsong.org for some background and a description of ways to help. Basically, volunteers are asked to try to get a good look at a singing bird to determine its gender, then make an audio and/or video recording with their cellphones. This information should be sent to major bird information collection sites, such as eBird or Xeno-canto.

Truth to tell, in a number of species, telling a male from a female bird is next to impossible. Black-capped chickadees, gray catbirds, cedar waxwings and blue jays come to mind. So it might be best to start with species where it’s easy to tell genders apart, such as Northern cardinals, many kinds of warblers and birds like rose-breasted grosbeaks and house finches.

This project should be easy and fun to do, and as long as you don’t interfere with a bird’s activity in order to record its song, you’ll have the comfort of knowing you’ve added to our knowledge of the avian world.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net.