By Nala Rogers
Posted on August 30, 2016
A new visualization tool for radar data is revealing bird migrations as they have never been seen before. With the new tool, birds’ nocturnal journeys appear as blue streaks that sweep across a map like raindrops on glass.
“[Songbirds] all travel at night, or almost all of them. So most of the migration, in fact, you can’t even see,” said Judy Shamoun-Baranes, an ecologist at the University of Amsterdam and first author of the study published yesterday in PLOS ONE. “You’ll only see them coming in in the morning, maybe, and landing, or you’ll suddenly see birds that weren’t there the day before.”
Humans may have difficulty seeing in the dark, but radar stations — the same ones that track weather or enemy aircraft — pick up signals from birds regardless of whether the sun is shining. Radar detects objects by sending out radio waves and measuring how long they take to bounce back. Birds move differently than drifting objects like seeds, and with the right software, researchers can isolate signals from large numbers of birds moving together. These signals contain information about how fast birds are moving, what direction they’re traveling and approximately how many are in the air. But the information is so complex that it can be hard to interpret, especially over large areas with multiple radar stations.
“For us, what’s always difficult is that you’re trying to integrate all of that information at once,” said Shamoun-Baranes. “You want to be able to tell a story, in a relatively simple visualization, which really gives you this feel for the flow of movement across a large landscape.”