Bill Hilton, Jr., executive director of the Hilton Pond Center for Piedmont Natural History near York, S.C., provides the following answer:

THE SECRET LIVES OF BIRDS, such as this Connecticut Warbler, can be explored using data collected from banded individuals.

For hundredsperhaps thousandsof years, casual observers have noticed the seasonal movements of birds. Early observers speculated about where birds went after departing each fall, but until fairly recently no one knew for sure.

All that changed in 1899 when Chris Mortensen of Denmark, a high school biology teacher, captured European Starlings in his backyard and placed metal rings on their legs. Each ring was inscribed with a unique number and instructions to correspond with Mortensen if one of his birds was found. In short order, marked starlings were being recovered across Europe andas folks wrote to inquire about the ringsMortensen and the scientific community realized how valuable ringing could be in helping to understand bird movement. This practice of capturing and marking birds crossed the Atlantic in about 1910, but here it has always been called "banding" instead of "ringing."

Today the Bird Banding Laboratory of the U.S. Geological Survey authorizes the work of about 3,000 licensed bird banders. Many are affiliated with state or federal wildlife agencies; others are independent researchers, university professors or graduate students. Together they band more than a million birds every year. Only about 2 percent of these birds are ever encountered again away from the original banding area, but that's enough to help ornithologists make reliable conclusions about bird migration, longevity, site fidelity, populations and behavior.

Hilton Pond Center for Piedmont Natural History in north-central South Carolina is a banding station where more than 34,500 birds have been banded from 1982 through March 2001. The following results illustrate the kinds of information that can be derived through a banding program:

-An immature male Hooded Warbler, banded in August 1987 at Hilton Pond during fall migration, was netted the following May on breeding grounds near Chapel Hill, N.C., by a graduate student studying this species. (Hooded Warblers overwinter primarily in Central America.)

-Two Pine Siskins, banded at York a year apart in the winters of 1987 and 1988, were re-trapped an hour apart in May 1988 at Duluth, Minn. (The straight-line air distance between Hilton Pond and Duluth is 990 miles.)

BANDS ARE ISSUED to all sorts of birds. This one encircles the leg of a Northern Saw-Whet Owl.

-A White-Throated Sparrow, banded on April 15, 1990, was caught and killed by a cat 970 miles away and only 16 days later at Lake la Ligne, Quebec. (Cats are responsible for far too many recoveries of banded birds.)

-A Purple Finch, banded at Hilton Pond (not far from the southern edge of its winter range) was found dead 1,660 miles away at Lewisporte, Newfoundland (the very northern limit of the breeding range for this species).

-A male Northern Cardinal that was banded at Hilton Pond as a juvenile male in July 1993 has been re-trapped several times each year since then, most recently in March 2001, when the bird was in its ninth year.

-Although Ruby-Throated Hummingbirds are banded at Hilton Pond from late March through mid-October, 40 percent of 2,315 hummers have been captured in the month of August.

Other banders have derived similar and even more amazing information though their research, but banding doesn't work unless the public reports the birds they find. Anytime a bird hits a kitchen window, for example, it's important for the homeowner to check for a band and report the number. The finder can contact a local bander, wildlife official or university biology department, or call the Bird Banding Lab toll-free at 800-327-BAND. By reporting a banded bird, the finder may help discover something brand-new about bird migration that just 100 years ago people could only speculate about.