Photo: Credit: NASA Earth

Blackbirds in Leipzig, Germany are staying up way past their bedtimes. Surrounded by light pollution, the birds are scrounging for food later into the evening than ever before, according to a study released by the Hemholtz Centre for Environmental Research.

It's well established that excess exposure to light jumbles birds' body chemistry. For instance, Western Scrub-jays' testosterone levels drop when they get too much light at night, throwing their mating cycles out of whack. But this new study explains how the glow of streetlamps and open windows can even disrupt bird behaviors as fundamental as eating.

Over five months, scientists observed the blackbirds in lit parts of the city and compared them to their counterparts in environments farther removed from manmade glare. They found that in March, when days were shorter, birds surrounded by light pollution kept eating for up to an hour longer than the control group. (You might think the extra feeding hours would make city birds fat. In fact, the scientists discovered that the citified group was no portlier in the aggregate than the forest dwellers, possibly due to the kinds of food available in each place.)

Reinhard Klenke and his team also found that male blackbirds kept later hours than females. The researchers chalked that difference up to the males' larger frames. "Larger eyes lead to better vision in poor light conditions," said Klenke, in announcing the results of the study. That means they can find food later into the evening—but there's a downside: It makes males more sensitive to the effects of extra ambient luminescence.

And that light is carrying ever outward as urban zones expand. Data from Loss of the Night, a citizen science project tracking the visibility of stars in the night sky, show that cities shine so bright that their halos spill far beyond the metropolis itself and into conservation zones. That problem will only grow, given that cities are set to grow by 2.5 billion people by 2050. Now you have one more reason to turn off that lamp.