Ornitho-logic

Chasing Birds Across the Country…for Science

A team of researchers radio-tags various species to learn more about them. The catch: They have to follow them as they fly.

Parked outside a cemetery in northwestern Illinois, antenna twirling atop her vehicle, Melissa Bowlin couldn’t help but look suspicious. When cops arrived to question her for the second time that day, she got so nervous she forgot how to spell the word “thrush.”

It’s all in a day’s work for Bowlin. She’s an assistant biology professor at the University of Michigan-Dearborn, and on that particular May day she was following a radio-tagged Swainson’s Thrush on its way north (the local law enforcement eventually realized she posed no threat and let her be).

Such run-ins with the police are commonplace for Bowlin, who’s part of an esteemed line of gonzo Midwestern researchers that attach radio transmitters to birds and then hop into cars or planes and chase them as they fly, tracking their movements and recording biometric measurements on the wing. Over the past half-century, they’ve filled in numerous gaps about bird migration and physiology—but virtually no one else in the world tracking birds actually chases after them as these guys do.  

“You have to be of a certain crazy mindset,” says Martin Wikelski, formerly of the University of Illinois and now director of the Max Planck Institute for Ornithology in Germany, “ready to go wherever” and then drive all the way back home days later. In order to collect data from the transmitters, the scientists must be somewhere between 3 and 18 miles away (the closer the bird is to the ground, the worse the radio signal; also, bigger birds can carry more powerful transmitters).

Chasing birds is no easy feat. Migrating songbirds often stay put for days at a time while rebuilding their energy reserves, and then take off suddenly. So researchers have to keep watch each night to make sure they don’t miss a departure. Then they have to keep up—despite weighing only an ounce, Swainson’s Thrushes, for example, can fly 45 to 50 miles per hour, and speed along at up to 70 miles per hour with a strong tailwind. Yet Bowlin swears the humans trying to keep up mind the speed limit on the ground. “We mostly stay on interstates,” she says. The most difficult spots to track are traffic-filled Chicago and the Illinois River (which birds cross without any regard to where humans can follow via bridge). But for the most part, the occasions when she loses birds’ signals are due to malfunctioning equipment rather than driving difficulties.

One of the trucks the researchers used to track. Photo: Melissa Bowlin/University of Michigan-Dearborn

Besides cops, Bowlin and her colleagues also field questions from curious passersby. The most common query? Whether they’re storm chasers, a la the movie “Twister.”

Bird chasing in the Midwest actually well predates the film, dating back at least as far as 1965, when Bill Cochran, an Illinois electrical engineer, developed a miniature radio transmitter light enough to attach to songbirds. “It’s amazing to think how much money he could have made,” says Wikelski, yet he gave the technology away “as a present to humanity.”

For decades, Cochran studied migration via these trackers, reportedly surviving a near-plane crash, a hairy situation in which he was confused for a drug runner, and a thunderstorm so severe he radioed in his will. “I was always driven by the desire to find out how birds find their way,” says Cochran. “Sort of unreasonable, like Captain Ahab and Moby Dick, except not as dangerous.” He tailed all kinds of birds, from raptors and nighthawks to swans, cranes, and geese, He focused most of his attention, however, on thrushes: Unlike many other songbirds, they don’t try to bite off radio transmitters. 

Over the course of his career, Cochran, now retired, helped prove that birds use the Earth’s magnetic field for navigation. He, and later Wikelski, also used radio transmitters to detect wing beat frequency, heart rate, body temperature, energy expenditure, and the vocalizations of migrating birds in flight. “You can measure those things continually—100 readings a second if you want,” says Wikelski, pointing out that no other tracking device allows that. Radio transmitters have also revealed bird migration routes (and to this day remain more accurate than geolocators and lighter than real-time GPS trackers).

In 1973, Cochran and an assistant followed a thrush for seven straight nights and 940 miles before finally losing it in Manitoba—a Cal Ripken-esque record not likely to be broken (they slept during the day when the migrant came down to rest). Today, thanks to tighter security between the United States and Canada, “it would take so long that we’d probably already have lost the bird by the time we got across the border,” Bowlin says.

But modern bird chasers do still pull all-nighters. Bowlin and her team spent each spring from 2011 to 2013 attaching radio transmitters to several Swainson’s Thrushes they had caught in a forest fragment near the University of Illinois. Hopped up on coffee, caffeine pills, and Mountain Dew, they then followed the migrating birds all night—and twice for two nights straight—with little clue as to where they would ultimately end up. In so doing, they discovered that the birds reached heights of up to 9,000 feet, and that they constantly adjust their altitude in flight, presumably in response to wind speed and direction. These results, published this August in The Auk: Ornithological Advances, came as a surprise: “I thought it was going to be really cut and dry—the birds go up, the birds fly for a while, the birds go down,” Bowlin says.

“A lot of people are jumping to the new things, the geolocators and so on, which are really cool, don’t get me wrong,” Bowlin says. But she’s not ready to give up the thrill of the chase.

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