Not all birds sing, but those that do — some several thousand species — do it a lot. All over the world, as soon as light filters over the horizon, songbirds launch their serenades. They sing to defend their territory and croon to impress potential mates.

"Why birds sing is relatively well-answered," says Iris Adam, a behavioral neuroscientist at the University of Southern Denmark. The big question for her was this: Why do birds sing so darn much?

"For some reason," Adam says, birds have "an insane drive to sing." This means hours every day for some species, and that takes a lot of energy. Plus, singing can be dangerous.

"As soon as you sing, you reveal yourself," she says. "Like, where you are, that you even exist, where your territory is — all of that immediately is out in the open for predators, for everybody."

In a new study published in the journal Nature Communications, Adam and her colleagues offer a new explanation for why birds take that risk. They suggest that songbirds may not have much choice. They may have to sing a lot every day to give their vocal muscles the regular exercise they need to produce top-quality song.

These findings could be relevant to human voices too. "If you apply the bird results to the humans," says Adam, "anytime you stop speaking, for whatever reason, you might experience a loss in vocal performance."

Just take a singer who's recovering from a cold or someone who has had vocal surgery and might need a little rehab. Adam says songbirds one day could help us improve how we train and restore our own voices.

A need to sing

To figure out whether the muscles that produce birdsong require daily exercise, Adam designed a series of experiments on zebra finches — little Australian songbirds with striped heads and a bloom of orange on their cheeks.

One of her first experiments involved taking males at the top of their game, and severing the connection between their brains and their singing muscles. "Already after two days, they had lost some of their performance," she says. "And after three weeks, they were back to the same level when they were juveniles and never had sung before."

Next, she left the birds intact but prevented them from singing for a week by keeping them in the dark almost around the clock. The only exception was a few half hour blocks each day when Adam flipped the lights on so the finches would feed and drink.

Light is what stirs the birds to sing, however, so she really had to work to keep them from warbling. "The first two, three days, it's quite easy," she says. She just had to move and they'd stop singing. "But the longer the experiment goes, the more they are like, 'I need to sing.'" At that point, she'd tap the cage and tell them to stop singing. They listened.

After a week, the birds' singing muscles lost half their strength. But Adam wondered whether that impacted what the resulting song sounded like. When she played a male's song before and after the seven days of darkness, she couldn't hear a difference.

But when Adam played it for a group of female birds — who are the audience for these singing males — six out of nine preferred the song that came from a male who'd been using his singing muscles daily.

Adam's conclusion is that "songbirds need to exercise their vocal muscles to produce top-performance song. If they don't sing, they lose performance, their vocalizations get less attractive to females — and that's bad."

This may help explain songbirds' incessant singing. It's a kind of daily vocal calisthenics to keep their instruments in tip-top shape.

"What they are highlighting is that you need a lot of practice to achieve a mastery in what you're doing," says Ana Amador, a neuroscientist at the University of Buenos Aires who wasn't involved in the research.

It's a good rule to live by, whether you're a bird or a human — practice makes perfect, at least when it comes to singing one's heart out.