How to Use Radar to Track Birds

Radars may be designed to track storms, but flocks of can birds show up too. Learn to use that to your advantage.

It was October 28, 2010, the night before the autumn birding festival in Cape May, New Jersey. There was only one problem: no birds. It was peak migration season, but in the preceding two weeks nothing had come through. The necessary winds had veered off course every evening just before nightfall, keeping the birds from beginning their journeys.

Back then David La Puma was a post-doc at New Jersey Audubon’s Cape May Bird Observatory. He recalls being at a potluck that night with about 20 other birders. Suddenly the folks hanging outside around the beer cooler started yelling: ‘There are bunch of Chipping Sparrows! You can hear them, they’re giving their flight calls!’  

Everybody ran outside. Soon they realized that it wasn’t only Chipping Sparrows; there were White-throated Sparrows; Fox Sparrows; Yellow Warblers. “This was big,” La Puma says.

The group watched the birds fly overhead. Then some of them turned to their computers, and to Doppler Radar—yup, the same radar we use for weather—and watched in excitement as the feathered storm developed.

“We look at the radar and you can see [the bird migration] start to bloom,” La Puma says, and then we can predict where the birds will be heading.

Once you start thinking about it, La Pluma explained, it’s no surprise that radar works for tracking migrating flocks. “These things pick up droplets of water in the atmosphere,” and compared to that, “birds are gigantic targets.”

La Puma, now the director of the Cape May observatory, says there are some limitations. For instance, it’s hard to know what size or type of bird is showing up on the radar, though that technology could improve soon.

When he was growing up surfing in Miami, La Puma used radar to predict wave conditions. He discovered the technology’s usefulness for tracking birds when he began his doctorate at Rutgers in 2004. As a grad student, there was little free time for birding, so when he did get a chance, he used radar to maximize it.

He was always keeping an eye on whether the birds are moving; If they are, is there anything to knock them down—rain, an opposing weather pattern? Are they being blown to the coast, where you’d expect to have coastal concentrations in the morning? Or are they being blown inland, so you’d expect to see them on the ridges? He soon started a website where he posted birding forecasts for New Brunswick and Somerset, New Jersey.

Six years later, on the night before the festival, he and his friends were furiously reloading the Doppler images, watching in real time as the green color that usually indicates a flock of birds turned into a thick yellow band that covered the entire area. When they jumped in their cars and headed to the coast, they couldn’t believe their eyes: “Birds you would never see in urban areas were walking around in the streets of Cape May,” La Pluma says. “It was insane.”

And it only got better. “The next morning it was just pandemonium,” La Puma remembers. “It was the first day of the birding festival and birds were dripping down trees, coming offshore, over the parking lots, filling every bush, landing on people.”

Much more pleasant than the other kinds of storms that radar detects.

Interested in learning how to use Doppler to maximize your birding experience? Start with this tutorial from La Puma:

After that, he advises checking out the synoptic weather maps posted weekly by Cornell Lab of Ornithology’s website, “It’s a great way to look at the radar, read the forecast, try to integrate the knowledge, and learn for yourself how all this works,” La Puma says, “...hopefully with enough time to get out there and find birds!”