Listening to Migrating Birds at Night May Help Ensure Their Safety
On autumn and spring evenings, hundreds of thousands, sometimes millions of birds migrate across North America. Cutting-edge recording devices are capturing the tiny chips and chirps these birds make while in flight, helping conservationists plot a protected course.
It’s a confusing vocabulary, and perhaps the greatest challenge to acoustic monitoring’s potential lies in the analysis of those ephemeral, scattered sounds. A single station on the mid-Atlantic coast could capture 5,000 recorded calls during a long October night. This fall Evans is monitoring 15 stations scattered across the continent. The project might generate 30 gigabytes of data per night—the equivalent of nearly 10,000 digital photographs—which would take Evans four hours or better to analyze.
“We’re talking about a crush of data, night after night during the migrations,” says Andrew Farnsworth, a research associate at the Cornell Laboratory of Ornithology. He should know. Farnsworth led the development of the so-called “Rosetta Stone for warblers,” a groundbreaking collection of spectrograms and photographs of 48 North American warblers’ night flight calls, and he is a leader on BirdCast, a joint effort to forecast bird migration. Cornell, with Oregon State University, the University of Massachusetts-Amherst, Microsoft, and the National Oceanic and Atmospheric Administration, hopes to site automated recording stations across the northeastern United States and along the Gulf Coast. “Extracting and identifying calls from thousands and thousands of hours of recordings is daunting,” Farnsworth says, “and computer scientists across the country are working on the algorithms needed to turn this data around quickly and meaningfully.”
Already acoustic monitoring is allowing researchers to ask increasingly specific questions about how migrating birds interact with the landscapes around them. Say it’s early fall, and you are a migrating scarlet tanager headed south from the boreal wilds of eastern Canada. While winging over eastern North America, the darkened earth below glitters with roadways, the twinkling of rural farmsteads, and small towns. To the east there is the onyx plain of the Atlantic Ocean. To the west is the relatively dark bulk of the Adirondacks. Then suddenly, studded with blinking lights and glittering glass towers that reach for 1,000 feet into the sky, the New York metropolitan region scrolls into view. Scientists know that migrating birds are attracted to artificially lit structures, such as communications towers and skyscrapers. And 70 percent of birds migrating to Canada from eastern North America fly over at least one urban landscape. When faced with an entire landscape shimmering like tinsel, what do birds do?
“Would you stay in the darker zones and fly to the west, tracking the Hudson River, or head east, along the East River, or go way over towards Jamaica Bay?” ponders Susan Elbin, director of conservation and science for New York City Audubon. At her office 15 floors above 23rd Street, Elbin, face ruddy from a recent trip where she was banding songbirds on nearby Prall’s Island, shares with migrating birds an altitude at which they are pre- sented with such difficult choices. “Would you just power on and try to gain altitude over all of Manhattan’s high-rises? Or would you careen through the skyscrapers? We don’t know how birds navigate these massively developed landscapes, and we need to know, because so much of the country is only going to become increasingly urbanized. Acoustic monitoring, coupled with radar, is the one tool that might finally give us some answers.”