Speedy birds flabbergast scientists

February 12, 2009 12:05:11 PM PST
Little songbirds cover more than 300 miles a day on their annual migrations, flabbergasting researchers who expected a much slower flight. For the first time, scientists were able to outfit tiny birds with geolocators and track their travel between North America and the tropics, something only done previously with large birds such as geese.

New tracking equipment, weighing only a little more than a paper clip, is now allowing the tracking of purple martins and wood thrushes, researchers report in Friday's edition of the journal Science.

"The migration was surprisingly fast," said Bridget Stutchbury, a professor of biology at York University in Toronto, Canada.

That's much faster than the 90 miles or so per day that had previously been estimated.

"We were flabbergasted by the birds' spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding. We always assumed they left sometime in March," said Stutchbury.

"I don't think anybody had an idea that these little songbirds could travel that fast," she said in a teleconference arranged by the National Geographic Society.

And they made better time going north in the spring than heading south in the fall.

Stutchbury said she believes the spring migration is faster because there are major advantages to arriving first on breeding grounds, including getting the best nesting spots, the chance to get high quality mates and to start breeding first.

"This is a breakthrough for understanding of bird migration and for conservation of smaller birds. I am surprised by the speed of flight, which is comparable to larger birds like the Pacific Golden Plover," said Helen F. James, a curator of birds at the Smithsonian's National Museum of Natural History.

"It's simply wonderful that we're going to be able to see these movements," said James, who was not part of the research team.

Indeed, the aim of the research is to understand how migration, and changes such as in climate and habitat, are affecting songbirds.

"Thirty species of songbird in North America show significant long-term decline," Stutchbury said. "We need to know whether it's the winter grounds or the breeding grounds driving these populations down."

In the study, wood thrushes and purple martins were captured in western Pennsylvania and fitted with the locating devices. The 1.5 gram clear plastic trackers sense and record sunrise and sunset, and when the birds return and are recaptured the data can be downloaded to a computer. Purple martins and wood thrushes weigh about 50 grams each - just under 2 ounces.

The timing of sunrise and sunset gives the location of the bird on each day of recording.

The tracking devices were placed on 14 wood thrushes and 20 purple martins during 2007 to track the fall takeoff, migration south, and journey back. In the summer of 2008, the researchers retrieved the geolocators from five wood thrushes and two purple martins. It wasn't clear what happened to most of the other birds, though Stutchbury said at least two were seen but the researchers could not catch them a second time.

The purple martins migrated to the Amazon basin in Brazil for the winter, while the wood thrushes wintered in a narrow band of Nicaragua and Honduras. Some of the birds took pauses along the way, spending a few days in the southeastern United States or in Mexico's Yucatan area.

Stutchbury said she initially worried that the tracking devices would slow down the little birds, "but those worries kind of ceased when I looked at their spring migration speeds."

She is now conducting further tests on these same species, and other researchers are doing similar tests in other small birds such as bobolinks, she added.

The research was funded by the Natural Science and Engineering Research Council of Canada, the National Geographic Society and the Purple Martin Conservation Association.