LULU GARCIA-NAVARRO, HOST:
Birds are heading south for the winter. Hundreds of millions of them take to the air across this country each fall, and we're currently in the peak of the autumn migration. NPR's Nell Greenfieldboyce reports that scientists, though, can now predict where and when the birds will be using a forecasting system that they call BirdCast.
NELL GREENFIELDBOYCE, BYLINE: Migrating birds typically fly at night, when there's fewer predators, and the atmosphere is more stable.
KYLE HORTON: So it's just this tremendous volume of birds, and it can vary even during peak season. You know, one night, maybe hundreds of millions of birds, and then significantly lower the next night.
GREENFIELDBOYCE: Kyle Horton is a researcher at the Cornell Lab of Ornithology. He says we know all this thanks to weather radar, which captures both raindrops and all those birds flying up there in the dark.
HORTON: We've known for a long time that radars can detect birds at night, and we've - you know, have been using them for nearly 75 years now to look at their movements.
GREENFIELDBOYCE: And what their movements show is that the birds respond to the weather - things like temperature and the wind. Birds will hunker down and avoid bad conditions like those created by Hurricane Florence. A rainstorm can just shut down migration.
HORTON: But right behind the storm can be really favorable conditions, so the migrants may take off as the storm sort of sweeps through.
GREENFIELDBOYCE: Horton and a colleague figured they could put all this radar information together in a new way. Their goal was to make predictions about bird migration to forecast which nights would see heavy bird migration and which nights wouldn't. They've created a system that's based on decades of radar data.
HORTON: And folks can go online right now and see an update and see what migration will be like tonight and then three days into the future.
GREENFIELDBOYCE: The BirdCast website has color-coded maps of the U.S. that look like the ones you'd see in a typical weather report - only in these maps, the areas of red and orange show the greatest number of birds. In the journal Science, the researchers say their forecasts are pretty accurate. Benjamin Van Doren is an ornithologist at the University of Oxford in the United Kingdom.
BENJAMIN VAN DOREN: Even seven days in advance, we're capturing in the forecast the majority of variation in migration that we see. So it gives us an idea even a week in advance what will happen.
GREENFIELDBOYCE: Having that much lead time is important, he says, because that could give people enough advance warning to take steps that could help protect migrating birds from some of the dangers they face on their journey.
VAN DOREN: For example, buildings with lights on that birds might collide with, communications towers with lights on that can pose a similar risk, wind turbines.
GREENFIELDBOYCE: All that stuff could be temporarily shut down during migration peaks. What's more, the forecasts are also helpful for people who just want to see the birds. Bird watchers have already started using the maps to decide when and where to go out looking for special birds that are passing through. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.