Tags turn up 3 tree swallows among 10 million

A tree swallow with the tagging device. (Credit: Teresa Pegan/Cornell)

A new tracking device allowed researchers to spot three tree swallows from Ithaca, New York, among the 10 million or so overwintering in Florida.

This feat was possible due to the first lifetime-solar-powered tag for small songbirds, an invention that could revolutionize the way birds and other small animals are tracked and studied.

“This is something we’ve been awaiting for 20 years: the ability to follow small birds throughout their migrations,” says the device’s creator, David Winkler, professor of ecology and evolutionary biology at Cornell University.

tree swallow with tag
Researchers place a solar-powered tag on a tree swallow. (Credit: Teresa Pegan/Cornell)

While large birds like eagles and ospreys can handle the extra cargo of a battery-powered tag, tree swallows themselves weigh only about half an ounce. To develop a lightweight alternative, Winkler collaborated with electrical engineers to create a tag powered by sunlight.

Their prototype consists of a solar cell and radio chip covered by a thin film of Mylar, with a wispy wire antenna that transmits the bird’s unique ID number to any receiver listening within about a mile.

Last summer, Winkler and his students tagged 70 tree swallows in Ithaca. Tree swallows are known to migrate to Florida and the Caribbean in the winter, so Winkler, former undergraduate students Teresa Pegan and Eric Gulson Castillo, and David Craig of Willamette University traveled to Florida in January, where they used weather radar to locate large flocks of tree swallows that might harbor tagged birds.

“The overwintering birds roost together at night in huge numbers—at times more than a million in one place,” Winkler says. “Leaving the roosts, they fly far up into the air in such large numbers that they are visible on weather radar.”

tree swallows overwintering in FL
Tree swallows in Florida. (Credit: dfaulder/Flickr)

Winkler and his team used weather radar to locate a flock foraging near Cape Canaveral. The birds were barely visible almost a mile away foraging low over a swamp, but the base station receivers picked up the pings from three different birds.

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This spring, Winkler and Pegan are once again on the search for the birds as the scientists study the round-trip migration in Ithaca. Previous banding studies in the 1990s showed surviving adults almost always return in successive years to the same site, whereas most first-time breeders disperse away from their home site, but usually no more than about seven miles.

The new technology should help scientists establish the behavior of these young birds on their first return migration, Winkler says. “Now, with autonomous base stations at all our nesting sites and a mobile unit to be driven around all the roads in our vicinity, we should get the best look at dispersal that we have ever had.”

The next step is to improve their ability to detect the signals. Winkler hopes his team can couple longer-range detection with the ability to pinpoint the location of the signal. He is keen to connect his tags with a network of stations up and down the East Coast placed by other researchers to track birds during their migrations.

Winkler expects the next generation of tags will be of interest to other wildlife biologists, an effort bolstered by a grant from the National Science Foundation. The tags are being commercialized through the Cornell Center for Technology Licensing.

Source: Amruta Byatnal for Cornell University