Bird Research 101
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A thick-billed vireo caught in a mist net.
Researchers use a calipers to measure the bill of a gray catbird.
Measuring the wing feather of a
gray catbird.
An ovenbird in a standard bander’s grip (researchers say they can feel a bird’s beating heart when they hold it like this).
A cotton swab is used to part the chest feathers of an ovenbird so researchers can assess fat deposits under the skin. If food is abundant, migratory birds will store considerable fat before starting their journeys.
Birds are placed head-first in a cardboard tube to keep their wings safely folded against their bodies before being weighed on a digital scale.
All photos © Layne Kennedy
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A thick-billed vireo hesitates before leaving the cardboard tube
in which it was weighed.
© Layne Kennedy
When I visited Eleuthera, its shrubs and low trees were alive with prairie warblers, gray catbirds and other wintering migratory birds. Thick-billed vireos, Bahama mockingbirds, Greater Antillean bullfinches and other West Indian species darted through the foliage. Ornithologists David Currie, Joe Wunderle, Dave Ewert and their field assistants want to identify each one…
But they also want to assess the birds’ physical condition and document sex and age. They want to mark individuals so they can be recognized later, either by sight or, in the case of Kirtland’s warblers, by radio signal. To accomplish these goals, the researchers can’t rely on binoculars alone. They need to capture birds.
And that, of course, is a task for professionals. Indeed, in the United States, it is against federal law to handle nongame migratory wild birds without a bird-banding, salvage or other special permit from the U.S. Geological Survey except under the direct supervision of a license holder.
Like bird banders the world over, the Kirtland’s warbler team uses special mist nets to capture live birds. Made of fine black nylon mesh and suspended from strings and poles, the nets look to human eyes like baggy badminton nets but are generally invisible to birds in flight. Those that struck the mesh while I was there hung in it unhappy but unharmed until they were quickly freed and transported to the banding station by assistants Ingeria Miller, Keith Philippe or another team member.
A quick inventory of a bird’s colors and patterns usually reveals its identity, sex and age, but some species require more careful examination. In such cases, size provides valuable clues. For the Kirtland’s warbler, researchers routinely take careful measurements of both the wing and bill. They use a thin ruler to assess the distance from the carpal joint to the tip of the longest wing feather and a calipers to measure the distance from the nares (nostrils) to the tip of the bill.
In-hand examinations can also yield crucial information about body condition. Immediately before migration, birds typically eat considerable amounts of food to put on fat that they use as an energy source while flying later. That fat often can be seen through the skin. Field researchers check for it by blowing back the breast feathers or by using a cotton swab to brush them aside. Along with a bird’s weight, which the Kirtland’s team acquires by means of a digital scale after gently tucking the animal into a cardboard tube, the presence or absence of fat speaks volumes about the quality of habitat.
Of course, one of the great benefits of capturing a bird is being able to mark it. Tiny, cylindrical bands of aluminum alloy, provided by the Geological Survey, are split lengthwise, positioned around a bird’s leg, then crimped together using special pliers. Most birds captured on Eleuthera receive such a band.
In addition to the metal band, each captured Kirtland’s warbler gets three brightly colored plastic leg rings. The colors can be viewed easily through binoculars, enabl-ing researchers to keep tabs on individual warblers without having to recapture them.
—Chuck Hagner
