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Go to Brilliant.org/SciShow to learn more about their Math History course. [♪ INTRO]. Stop for a moment and listen—do you hear any birds singing?

Bird songs are all around us and, at some point in school, you probably learned why. That story might’ve gone something like this: male songbirds sing to proclaim their intentions to potential mates and to warn off rival males. Dating all the way back to Darwin’s observations in the 1800s, birdsong has been described as a male trait shaped by sexual selection in competing for females.

The better or louder a male sings, the higher his chances of reproducing. But, wait—what about female birds? Don’t they sing too?

Many do, in fact, but there is a good chance that you have never learned about them. One 1986 scientific paper on the evolution of bird songs spent more than 20 pages and 170 references without a single mention of females singing. Many other papers aren’t much better, despite the fact that, in 71% of all songbirds, both males and females sing.

Now we’ll get back to why you’ve probably never heard this, but first: what are all these female birds saying? Like in males, the motivations for females to sing, or not sing, can be complex. But as with males, finding and retaining a mate is a major component.

Take the Alpine Accentor, found in the Pyrenees mountains. When they are fertile, females sing to attract males. When a male arrives, the singing female solicits sex.

And females sing less when males are guarding them. Plus, their songs draw in males but not other females. In the Alpine Accentor, female songs may also advertise her reproductive prowess.

Older females, who tend to lay bigger clutches, have more complex songs. Female birdsong might also play a role in maintaining a mate. For instance, while scientists historically believed that Eastern Bluebird females didn’t sing, a recent study has shown that they can use song to strengthen their pair bonds.

Bluebirds have higher reproductive success if they stay together for multiple nestings. So singing may help them retain their breeding partners; not too dissimilar to a date night in humans. And speaking of romance, lots of songbirds sing duets, in which they take turns singing back and forth.

Recent research of the Subdesert Mesite of Madagascar suggests those duets may do more than just help retain the attention of a male. Females start most of the duets, and males respond, a pattern that’s been linked to males guarding their mates. But, Subdesert Mesite females also respond in duets started by males.

So it looks like females are guarding their mates right back. And mate-guarding makes sense for these birds. Subdesert Mesites live in groups that together secure a territory to get the resources they need.

And in these mixed-sex groups, both males and females must be on alert for mate-stealing. But studies of female birds are suggesting that their songs are not always about males. If you hang out in the jungles of Puerto Rico, you might hear male Troupials belting out their solos before dawn during the breeding season.

But females hold the monopoly on year-round, daytime singing. Female Troupials duet with males, but also sing their own solos, which researchers suggest could help them defend their fruit and insect resources from other birds. And there are probably other reasons they sing, as well.

But what about the 29% of species in which the female doesn’t sing? Ornithologists are still figuring out why some female birds stay silent. One reason might be that singing can attract predators to the nest and endanger the young.

Scientists studying the Superb Fairywren found that males and females are quieter during incubation and chick feeding. And, when researchers set up fake nests and used a speaker to broadcast female songs, those nests lost more eggs to predators. Over time, that loss could provide an evolutionary pressure that selects against vocal females, especially for species in which the female spends a lotta time in the nest.

So why are we just figuring all of this out now, hundreds of years after we first started studying bird songs? Like many things in science, a lot of it comes down to history. Many of the early studies of birds were in temperate regions, such as the US and the UK, where the ornithological societies of the 1800s were founded.

We now know that tropical species are much more likely to have singing females than temperate ones, so that was just kinda bad luck. But the sexism that permeated early science and remains stubbornly common was perhaps the biggest obstacle. It wasn’t that nineteenth century women weren’t thinking about why birds sing; their male peers just weren’t taking them seriously.

And male ornithologists, working in a male-oriented world, were primed to see male birds as the main driver in the evolution of birdsong. Interestingly, as women have broken into the field of ornithology, they’ve also expanded research into female birds. A recent literature review found that women make up the majority of first authors on female birdsong papers in the last 20 years, but are the minority of ones that study birdsong more generally.

This attitude shift is affecting more than just singing. Modern ornithologists are also revisiting the way female birds look, which may have its own evolutionary pressures independent of males. It’s a reminder of some of the enormous blindspots science has suffered, thanks to a lack of diversity.

As we break down our biases in science, who knows what we will discover next? Likely, no matter what it is, we will do it while listening to some beautiful birds sing. Because they’re always around, making good sounds.

And if you’d like to learn more about how past discoveries shape our present understanding, you might enjoy Brilliant’s course on Math History. Because math didn’t just emerge from some font of pure knowledge, it had to be developed and discovered by people. In this in-depth course, you can learn more about their legacies, and the questions they left unanswered.

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