Tracking Device Reveals Songbirds' Travels

Bridget Stutchbury releases a purple martin. i i

Biology professor Bridget Stutchbury of York University in Toronto releases a purple martin outfitted with a tiny geolocator for its round-trip migration. Of the 34 songbirds outfitted with the devices, two purple martins and five wood thrushes returned to their starting place in Pennsylvania, allowing scientists to reconstruct their routes. John Tautin/Purple Martin Conservation Association hide caption

itoggle caption John Tautin/Purple Martin Conservation Association
Bridget Stutchbury releases a purple martin.

With hopes of recapturing the bird next year, biology professor Bridget Stutchbury of York University, Toronto, releases a purple martin outfitted with a tiny geolocator for its round-trip migration. Two purple martins — as well as five wood thrushes — returned to their starting place in Pennsylvania, allowing scientists to reconstruct their routes. The research was partly funded by National Geographic.

John Tautin/Purple Martin Conservation Association
A male wood thrush with geolocator feeds its young. i i

A male wood thrush feeds its young while wearing a miniaturized geolocator backpack. Fourteen wood thrushes wore the devices for the long trip to the tropics and back in groundbreaking research on songbird migration, led by Stutchbury and partly funded by National Geographic. Elizabeth Gow hide caption

itoggle caption Elizabeth Gow
A male wood thrush with geolocator feeds its young.

A male wood thrush feeds its young while wearing a miniaturized geolocator backpack. Fourteen wood thrushes wore the devices for the long trip to the tropics and back in groundbreaking research on songbird migration, led by Stutchbury and partly funded by National Geographic.

Elizabeth Gow
A female purple martin outfitted with a geolocator device. i i

A female purple martin wears a geolocator device. Twenty purple martins, members of the swallow family, wore them while migrating from Pennsylvania to South America and back. The birds made the trip three times faster than expected. Timothy J. Morton hide caption

itoggle caption Timothy J. Morton
A female purple martin outfitted with a geolocator device.

A female purple martin wears a geolocator device. Twenty purple martins, members of the swallow family, wore them while migrating from Pennsylvania to South America and back. The birds made the trip three times faster than expected.

Timothy J. Morton
A female purple martin wearing a geolocator. i i

A female purple martin wears a miniaturized geolocator backpack and leg bands. The bird was one of 34 songbirds outfitted with the devices so that York University researchers could track their fall and spring migration for the first time. A color-coded band helps researchers identify the bird on its return to the Purple Martin Conservation Association's research colony in Pennsylvania. Timothy J. Morton hide caption

itoggle caption Timothy J. Morton
A female purple martin wearing a geolocator.

A female purple martin wears a miniaturized geolocator backpack and leg bands. The bird was one of 34 songbirds outfitted with the devices so that York University researchers could track their fall and spring migration for the first time. A color-coded band helps researchers identify the bird on its return to the Purple Martin Conservation Association's research colony in Pennsylvania.

Timothy J. Morton

For the first time, biologists say they've actually been able to track individual songbirds from their North American breeding grounds down to their winter haunts in Latin America, and back again.

Ornithologist Bridget Stutchbury at York University in Toronto and her colleagues used a gizmo invented by researchers at the British Antarctic Survey, called a geolocator. The device weighs half as much as a dime.

"These devices measure light, so you put them on the bird's back like a little backpack, and off the bird goes on migration," Stutchbury explains. "And when it comes back the next spring, you catch the bird, take the backpack off, and download the data onto your computer."

The computer can analyze a daily record of sunrise and sunset the birds experienced during their migration, and get at least some idea of where the birds have been. The accuracy isn't great — they can only locate a bird to within a few hundred miles — but that's still useful information.

Debunking Old Assumptions

Writing in the Feb. 13 issue of Science magazine, Stutchbury and her colleagues say they managed to track five wood thrushes from Pennsylvania to Central America, and back again.

They also followed the flight of two purple martins, which is a type of swallow.

"I was surprised that both of them spent most of the winter in the Amazon Basin," Stutchbury said. That's because up north, martins usually fly over wide-open fields, catching insects on the wing. But in winter, for some reason, they seem to head for the woods.

Even more surprising was how fast they high-tailed it home. "The flight times were amazing," she said. "We had a purple martin that over-wintered near the Amazon River in Brazil, and it flew back to its breeding colony in the northern U.S. in only 13 days. This is incredible. I had no idea that songbirds could go this fast."

Also surprising was the flight path of one of the wood thrushes she tracked. Ornithologists assumed that these birds flew straight home from Latin America, right across the Gulf of Mexico. Four of the tracked birds did. But the fifth bird Stutchbury followed actually took the long way around, flying up the coast of Mexico.

"Presumably this bird was in poor condition, and flying across the Gulf of Mexico requires a 12-14 hour nonstop flight over water," she said. "And if the birds run out of steam over the Gulf of Mexico and go into the water, they're doomed. They're going to die."

This first successful experiment with songbird backpacks isn't simply a matter of curiosity. Stutchbury and other ornithologists are trying to figure out why some species of North American songbirds are in distress. Is it trouble here on their breeding grounds, or trouble down south?

Future Of The Device

Pete Marra at the Smithsonian Migratory Bird Center at the National Zoo says these tracking devices could help them solve that mystery.

"I actually think the floodgates are open now. And I think a lot of people are going to be deploying these on as many species as they possibly can. I'm going to be putting them on 100 wood thrushes this year, across their entire range."

That could provide a clue about why one of the most melodious denizens of the northern woods is slowly fading away.

But Marra adds that the devices are far from ideal, since they can't pinpoint a bird's location.

"There's still a lot of work to be done to try to miniaturize this tool even a bit more and put some other gizmos on, such as ones that would allow us to record temperature or altitude or relative humidity."

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