By Juliet Eilperin
Washington Post Staff Writer
Friday, February 13, 2009
In the summer of 2007, a team of scientists devoted its mornings for several weeks to attaching tiny data chips encased in clear plastic to the backs of nearly three dozen songbirds they had trapped in northwestern Pennsylvania.
As one researcher held each bird still, another would slide a Teflon loop around one of the animal's legs -- in much the way that a parent slips a backpack over a child's shoulders -- before working a second loop around the other leg and then stitching the chip and loops together with Kevlar thread.
Set free, the 14 wood thrushes and 20 purple martins took off that fall on their epic seasonal voyages to South America, with the "geolocators" resting comfortably on their backs.
When the prodigious flyers returned last spring to breed, the scientists were able to find and trap seven of the 34 birds again and recover the chips, reaping a harvest of data that is stripping away many of the mysteries of the annual migrations, revealing not only the animals' routes and resting places but the remarkable speed at which they can travel.
Providing details that have eluded scientists for years, the team of Canadian, American and British researchers describe their findings today in a report published in the journal Science.
They found, for example, that some birds flew as far as 311 miles in a day, typically traveling faster on the northward journey. One especially energetic purple martin, a member of the swallow family, flew 4,650 miles from its wintering grounds in Brazil to its breeding site in Pennsylvania in just 13 days.
"I don't think anybody had any idea these little birds could fly that fast," said the report's lead author, Bridget Stutchbury, a biology professor at Canada's York University. She noted that previous studies had suggested songbirds traveled only a third as fast. "This is the first time anyone has been able to map songbird migrations to the tropics and back," she said.
The research, funded in part by the National Geographic Society, underscores how technological advances are giving scientists new insights into how animals move, feed and behave, in the air and the sea as well as on land.
Until now, researchers were able to track songbird migrations only by sight, by radio monitoring, by observing flocks pass by on weather radar or by trailing the birds in planes. In each case, the tracking did not last longer than four days.
While scientists have previously been able to monitor large birds such as peregrine falcons and geese by fitting them with satellite transmitters, that equipment is too large for songbirds. So Stutchbury, working with experts at the British Antarctic Survey, refined a device that records light data and weighs just 1.5 grams, less than a dime. The birds weigh on average 50 grams each.
The researchers placed a recorder at the base of each bird's spine so it would not interfere with the animal's balance, breeding or feeding of its young.
The devices could not transmit data in real time, but they recorded the exact time of sunrise and sunset, allowing the researchers to download the data later and calculate where each bird was on any given day.
The geolocators not only showed how fast the birds flew but when and where they stopped. The southbound purple martins, for example, took a break in the Yucatan for three to four weeks before heading on to Brazil.
One northbound wood thrush, opting for the scenic route, took 29 days to fly 2,852 miles, choosing not to cross the Gulf of Mexico. The fact that it did not attempt the more than 12-hour nonstop crossing, Stutchbury said, could indicate that it was underfed and tired because its wintering grounds in South America had become degraded. Future monitoring, she said, "could help us understand how forest fragmentation and habitat quality affect the journeys of these songbirds."
Stuart L. Pimm, Duke University's Doris Duke professor of conservation ecology, said the new research "adds a hugely important piece of the puzzle" of bird migrations and will help scientists "protect migratory songbirds as they go to and fro each year."
Scientists have become increasingly concerned about the future of songbirds as their populations have dropped worldwide over the past four decades. Wood thrushes have declined 30 percent during that period.
Scott Edwards, a Harvard University biologist and curator of ornithology, said the study has "really opened up a new threshold in our study of avian movements." The data will help bolster conservation efforts now that experts know where songbirds "put down and refuel" during migrations, he said.
As researchers come up with ever more miniaturized tracking equipment, Edwards said, "things are just getting smaller and smaller and lighter and lighter, and eventually we'll be looking at embedded microchips."
Stutchbury said "there's no sign at all" that the songbirds "even know they're wearing the backpacks."
She said her team is hoping to collect more data this spring; it placed geolocators on 20 more purple martins and 35 wood thrushes in 2008.
The scientists still do not understand why they were able to recapture only two of the purple martins last year, but Stutchbury said they will continue to pursue the research unless they find out this year that only a few purple martins return.
"There is no other way to do this right now," she said.