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."