Birdie Backpacks

A purple martin wearing a geolocator. Photo courtesy of Tim Morton.

Birds are most famous for their flying ability. Man has never really been able to crack the mystery of flight and migration. Now we may be one step closer to being able to track these migrations and discover some of the subtler points of them.

Researchers have come up with a tiny birdie backpack that contains sophisticated sensors; yet, weighs less than a dime. While the new technology has already yielded interesting data such as some birds fly faster than previously thought; it’s real worth will be in unlocking the mysteries of bird migration that could help preserve species threatened by habitat loss and climate change.

“We knew that purple martins went to Brazil and wood thrush went to Central America,” said Bridget J. M. Stutchbury, a biologist at York University in Toronto, who with the aid of colleagues fitted birds from these species with the sensors and mapped their migrations last year. “But the details of how an individual gets there, what routes they take, how fast they fly, how often they stop to rest — these are the kinds of details we have never been able to have.”

As The Bird Flies - A Graph

The tiny backpacks contain solar geolocators that collect and store data on the birds’ location based on their relation to the sun. When the sensors are removed, the information is downloaded and this tells researchers when and where the birds have been.

“If the bird were on a hillside you’d get a slightly wrong time,” Dr. Stutchbury said. “If it were a cloudy day you would get a slightly wrong time. But these devices are accurate enough, within 5 or 10 kilometers (3-6 miles)”.

Engineers at the British Antarctic Survey developed this system for tracking Wandering Albatrosses. These birds are the largest of the albatross family and inhabit the waters around Antarctica. Unfortunately, the Wandering Albatross is about the size of a large dog; so, the sensors made for them were obviously too large to be used on songbirds.

British researchers announced at a conference in 2006 that they had miniaturized their sensors to 1.5 grams. “That for me was a magic number,” Dr. Stutchbury said. “I could put it on a large songbird.”

Dr. Stutchbury has managed to obtain sensors that weigh even less than 1.5 grams and sit on the bird’s back at hip level. Each sensor is about the size of person’s pinkie nail. “There’s a little loop that goes around each leg,” she said. “It would be like you wearing a backpack.”

Researchers used nets to trap 34 birds in Pennsylvania in the summer of 2007. Sensors were applied to the birds after determining they were in a healthy condition and acting normally. They were then released and the scientists waited for the end of the migration approximately one year later.

April 25, 2008 was the day the first bird with a geolocator returned to Pennsylvania. “It seemed almost a miracle,” Dr. Stutchbury said.

Some of the information gleaned from the recovered geolocators show the birds flew two to six times faster going north than south. Some birds covered about 370 miles in a day which is much faster than was previously though. One female martin flew almost 5,000 miles in 13 days – including 4 stopover days.

Dr. Stutchbury identified the Yucatan Peninsula as being an important stopover point in these migrations. She and other experts say identifying important migratory stopovers will be an important benefit of the technology.

Since data from only seven of the 34 tagged birds was recovered, Dr. Stutchbury and her colleagues have tried not drawing too many conclusions from the data. However, she points out, “That’s seven more than anybody else.”

Last summer, she and her colleagues applied sensors to dozens more birds. The work is important, she said, because songbird species are already in steep decline and climate change may threaten crucial habitat.