Migrating songbirds get home fast in spring: study

WASHINGTON (Reuters) - Migrating songbirds can get back up north to their breeding grounds in astonishingly quick time, with some traveling up to 360 miles a day, researchers reported on Thursday.

They designed tiny geo-locators that they fitted to purple martins and wood thrushes with lightweight backpacks to track them as they traveled between the United States and either Central America or Brazil.

Data from the birds they were able to find and trap showed that while they mosey south in the autumn, they race north in the spring, perhaps to snag the best nesting sites and mates, Bridget Stutchbury of the University of York in Toronto and colleagues reported.

"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," a pace of nearly 360 miles a day, they wrote in a report in the journal Science.

Previous estimates had put the pace at only about 150 km or about 90 miles a day.

"This is the first time that anybody has been able to map songbird migrations to the tropics and back," Stutchbury told reporters in a telephone briefing.

The tiny geo-locators record light to track the birds' latitude and longitude. Because transmitters are too large to put on a little bird, the devices had to be collected to retrieve the data, Stutchbury said.

She said the device and backpack weighed 0.05 ounces (1.5 grams). "These things are lighter than a dime," she said.

The questions answered are important for conservation, Stutchbury said. "Songbirds around the world have plummeted in numbers in the past 30 to 40 years," she 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," she added.

She said the birds could catch flies in the air, breed and lay eggs while wearing the backpacks. Nonetheless, the researchers are designing even smaller devices for their next round of study.

The study, funded in part by the National Geographic Society, also showed the thrushes traveled in flocks, wintering together in a tight band and then returning to the same places in spring.

(Editing by Michael Kahn and Sandra Maler)