Artificial light has essentially lengthened birds' day

Analysis of millions of birdsong recordings from over 500 species across multiple continents combined with satellite light‑pollution and sunrise/sunset data shows that artificial night lighting lengthens bird active periods by about 50 minutes on average. Birds start vocalizing roughly 20 minutes earlier and stop about 30 minutes later, effectively extending daily routines. Backyard monitoring devices in the BirdWeather program automatically register and identify calls, creating a massive activity dataset. Artificial lighting can also send migrating birds off course and has been linked to nighttime feeding in some species. The ecological consequences for survival and reproduction remain uncertain.

The early bird gets the worm, as the old saying goes. And now a lot of birds around the globe are starting their days earlier than ever, because of unnaturally bright skies caused by light pollution. "For these birds, effectively their day is almost an hour longer. They start vocalizing about 20 minutes earlier in the morning and they stop vocalizing about 30 minutes later in the evening," says Neil Gilbert, a wildlife ecologist with Oklahoma State University.

Scientists already knew that light pollution affects birds. It can send migrating birds off course, and some observations have linked artificial lighting to unusual bird activity, including one recent report of American Robins feeding their babies in their nest at night. But Gilbert and Brent Pease, with Southern Illinois University, took a more comprehensive view, by analyzing millions of recordings of birdsong.

The audio was collected by thousands of devices installed in backyards and other locations, mostly by birdwatchers and other wildlife enthusiasts, as part of a program called BirdWeather. The BirdWeather devices automatically register bird calls and use them to identify the species, mostly to let bird fans know what's flitting through their yards. At the same time, however, the project is also accumulating a huge set of basic data on bird activity.

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