February 13, 2009

Scientists Astonished By Small Bird Migration Speeds

For the first time, scientists have been able to track a tiny outfit of songbirds to study their annual migrations between North America and the tropics. 

Researchers were astonished to discover that the purple martins and wood thrushes flew more than 300 miles a day during their migrations.  The number was much higher than the 90 miles per day that researchers estimated.

According to a report in Friday's edition of the journal Science, the researchers were able to equip the birds with tiny tracking devices that weighed slightly more than a paper clip. 

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

"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," she said in a teleconference arranged by the National Geographic Society.

The researchers were also surprised to discover that the birds traveled quicker while going north in the spring than heading south in the fall.

According to Stutchbury, the spring migration could be faster because of the advantages afforded to those who arrive on breeding grounds first, including high quality mates, and better nesting spots.

"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, of the Smithsonian's National Museum of Natural History.

The aim of the research is to have a better understanding of how changes in climate and habitat affect songbirds.

"Songbirds around the world have plummeted in numbers in the past 30 to 40 years," Stutchbury said. "In order to stop those declines, we have to understand whether it is the breeding grounds or the wintering grounds that are causing the major problems."

To gather information on migrations, the researchers fitted wood thrushes and purple martins in Pennsylvania with locating devices.  The tiny plastic devices could record sunrise and sunset.  The data was recaptured and downloaded when the birds returned to Pennsylvania.

Because the devices recorded sunrise and sunset, researchers were able to track the latitude and longitude of each bird.

The devices were placed on 14 wood thrushes and 20 purple martins in 2007.  When the birds returned in 2008, the researchers were able to retrieve the locators from two purple martins and five wood thrushes. 

According to Stutchbury, two other locators were seen on birds, but the researchers were unable to capture the birds a second time.

The data showed that the purple martins migrated to the Amazon basin in Brazil during the winter, while the wood thrushes headed for Nicaragua and Honduras.

"One female martin left the Amazon basin after the night of 12 April and flew about 7,500 km (4,660 miles) in 13 days," the researchers wrote in the report. At that speed the bird was traveling nearly 360 miles a day.

Some of the birds took breaks along the way in the southeastern United States or in Mexico's Yucatan area.

Researchers were initially worried that the devices would weigh down the tiny birds, but according to Stutchbury "those worries kind of ceased when I looked at their spring migration speeds."

Stutchbury is now conducting more research on the little birds, while other researchers have begun to study other small species.

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


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