Unraveling migration's mysteries

On a bahamian island, an ornithologist and helpers clamp tiny, numbered anklets on birds

Last month, I was a "citizen scientist" in the Caribbean. About a dozen people from across the United States flew to the island of Andros to be ornithologists (or-nih-THOL-uh-jists) - bird scientists - for a week.

We stayed at a resort that's usually filled with scuba divers. We scoured the eastern edge of the island, counting the number of bird species we saw. (I saw 104!)

More important, we helped scientists keep track of wild birds by catching them; putting tiny, numbered bands on their legs; and letting them go.

Mike Baltz was our leader. He is one of the 6,000 or so people in the US who have been specially trained and licensed by the government to band birds. (You can only buy bands from the government, and you can't buy bands without a license.)

Dr. Baltz first came to the island 10 years ago as a dive master (an accomplished scuba diver). But when his interest turned from fish to birds, he realized Andros was the perfect laboratory in which to study the tiny warblers that spend winter there.

"Ring it and fling it," Baltz said. "That's what the British say when they're banding birds." We all sat in chairs set in the shade of the van and watched the ornithologist use special pliers to bend a tiny aluminum band around the leg of a northern parula. He then stretched out one of the warbler's wings and measured it with a caliper (a special ruler).

As he took measurements, he called out the numbers, which were recorded on a piece of paper in his metal clipboard. Baltz also checked for body fat by blowing on the bird's chest feathers and looking for yellow fat deposits visible beneath the skin. He tried to determine the sex and age of the bird - not always an easy task. Finally, he weighed each bird by placing it headfirst into a film canister attached to a spring scale.

The northern parula weighed a little more than 6 grams. That's about what a quarter and a dime weigh together.

When Baltz released it, the warbler flew to a low branch in a pine tree, picked at its new aluminum anklet, and scolded us. (The birds quickly get used to the loose, lightweight bands.)

Then we headed for the series of "mist nets" we had set, to check for newly trapped birds. Earlier, several of us had helped Baltz put up these long, thin nylon-mesh nets in a forest clearing. The nets stretched almost from the ground up to higher than I could reach. Each had four long pockets that extended the length of the net. When birds flew into the nearly invisible net, they fell into one of the pockets.

Most birds fall onto their backs. When they're in that position, birds tend not to struggle. Some do, though, twisting themselves this way and that. We carefully untangled them.

Bill Mossey, a birder from Long Island, N.Y., was on the trip. He was nervous about handling the birds at first. They seemed so delicate, and he didn't want to hurt them. "But I quickly learned that, for all their seemingly fragile nature, they are far more hardy than I first thought," he says. And some of them can peck you pretty hard with their beaks, if you're not careful.

We spent hours walking from one net to the next, retrieving birds. You never knew what you'd find: a delicate worm-eating warbler, perhaps, or a Greater Antillean bullfinch with a finger-grabbing beak.

Once we even found a fish - or rather, a large piece of one - in the topmost pocket of a net. All we could figure was that a turkey vulture had dropped its lunch.

For four years, Baltz has been collecting data on the birds he's banded in this remote forest. Last year, more than 1.2 million birds were banded by US-licensed bird banders. The data on each was sent to the Bird Banding Laboratory (BBL) in Maryland.

The bands have a serial number and a phone number to call, in case a band is found. Only 1 or 2 percent of the bands are recovered. But where the bands turn up can say a lot about where a bird has been.

Baltz hopes the information he gathers can help him understand the biology and ecology of the warblers that come to Andros in the winter. By documenting long-term trends in Neotropical migrants (birds that migrate to the Western Hemisphere's tropics for the winter), researchers like Baltz hope to find out whether these bird populations are declining and, if so, why.

"We see a lot of problems with habitat loss on the wintering grounds," Baltz says. The forest is cut for lumber or cleared for houses or ranches.

"But we have to look at all parts of their range," he adds. "In the breeding grounds in the north, forest fragmentation is a huge problem" - there are fewer large, unbroken patches of forest. "We're seeing habitat loss along migration routes as well." Birds need safe places to rest and eat on their long journeys.

As we checked the nets, Baltz talked about different warbler habitats. Just then we came upon an ovenbird in a net. It already had a tag on its leg. As I untangled the bird and read the number to Baltz, he checked it. This bird had been in this 200-yard stretch of forest before. It must really like it here, too. This was the third year it had been caught in one of Baltz's nets!

WEBSITES

Bird Banding Laboratory

www.pwrc.nbs.gov/bbl

US and Canadian government site has banding history, statistics, how to report a bird band, and lots more.

BIRDNET

www.nmnh.si.edu/BIRDNET/index.html

The Ornithological Council hosts this site with links to member societies.

Bird Source

birdsource.cornell.edu

The Cornell Laboratory of Ornithology and Audubon sponsor this feature-packed site. Join the Great Backyard Bird Count, Feb. 16-19.

Partners in Flight:

www.partnersinflight.org

PIF works to preserve bird habitats in northern breeding grounds and southern winter ranges.

(c) Copyright 2001. The Christian Science Publishing Society

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