It seems like every day there’s a new warning about how looking at brightly-lit screens before bed can mess with our sleep.

It turns out humans aren’t the only ones.

Birds in brightly-lit areas are also extending their singing hours, researchers just reported in Science Advances.

The findings are one more piece of evidence for the myriad ways light pollution is messing with the behavior of birds and other animals. It’s also an illustration of how cheap audio recorders and powerful computers are giving scientists new insights into ecosystems.

“We were shocked by our findings,” said Brent Pease, an ecologist at Southern Illinois University. “Under the brightest night skies, a bird’s day is extended by nearly an hour.”

The difference between night and day is one of the most basic drivers of biology, and the proliferation of artificial lights is upending that predictable solar rhythm. So it’s no surprise that both plants and animals are reacting. City lights can lure migrating birds into colliding with buildings, cause mountain lions to avoid habitat, and make plants grow more.

It might seem like common sense that all this extra light would also affect when birds strike up a tune. Anyone who’s gone for a walk in the woods at sunrise or sunset will have heard the dawn or dusk chorus, when many birds are at their most exuberant. But past studies have produced mixed results. Some studies found light pollution caused birds to start singing earlier in the morning. Others showed a much weaker effect.

Then, Pease stumbled onto a vast trove of largely untapped data about birds’ singing behavior. To give people at the university a little more exposure to the natural world, he set up an audio system joining the campus in Carbondale, Illinois with the Touch of Nature Outdoor Education Center, 8 miles away. That system, BirdWeather, pairs microphones with a sophisticated computer program that can identify some 6,000 species of birds based on their birdsong. It’s the same system powering the popular bird ID phone app Merlin.

“We started seeing—in real time—which birds were at Touch of Nature, right in our Agriculture Building,” he said. “I realized that I stumbled upon something really important for wildlife research. All of a sudden, we not only know where species are but how they are behaving 24/7.”

BirdWeather offered a much bigger view than a single place in Illinois. Pease and his collaborator, Neil Gilbert of Oklahoma State University, were able to retrieve a massive planet-wide dataset containing 2.6 million hits on 583 different species of daytime (not nocturnal) birds in 7,824 locations between March 2023 and March 2024.

To find patterns in this mountain of data, the two used computer programs to sort and then match it with satellite data tracking patterns of light pollution across the globe.

The duo discovered that birds in places with large amounts of light pollution were singing, on average, nearly an hour longer than their counterparts in darker places.

That doesn’t mean every bird species reacted the same way. Some, it turns out, are more likely to change their singing habits. Bird species with larger eyes, for instance, had a stronger response.

“We had the idea that maybe it was a species’ photoreceptor sensitivity—their eyesight. And this turned out to be a key factor,” said Pease. “Species with large eyes relative to their body size had a disproportionately stronger response to artificial light at night.”

Birds that nested in the open also tended to extend their singing times around artificial lights far more than ones that nest in cavities, perhaps because they are more sheltered from the glare.

What’s not clear is whether this extended party time is helpful or harmful for the birds. It could be leaving the birds fatigued or stressed from the extra carousing, say the researchers. Or it could be that these birds are getting a leg up, with extra time to attract a mate or forage for food. After all, you know what they say about the early bird.

Pease, et. al. “Light pollution prolongs avian activity.” Science Advances. Aug. 21, 2025.

Photo: Unsplash+