If you hunt ducks or geese long enough, and harvest many—or are just fortunate—you may harvest one with an aluminum band on one leg, fastened like a bracelet above its webbed foot. It’s a rarity, because only a small number of waterfowl are ever banded by biologists or the technicians who assist them.

You will probably see more leg bands in print than in person, in photo-illustrated ads selling equipment for duck and goose hunting, like shotguns, ammunition, calls, clothing or other gear. The bands will typically be strung like beads on a lanyard that holds a waterfowler’s duck or goose calls, this lanyard being a standard item of hunting accoutrement. By marketing logic, the bands imply hunting success and prowess, and the gear being advertised just might have had something to do with it. Or so the ads suggest.

The purpose of these leg bands is to help biologists understand the patterns of duck and goose migration, the routes they travel and where they over-winter. When—or more probably, if—a band is recovered, the person who recovers it will hopefully call the toll-free number engraved on it, this being the number for the federal Bird Banding Laboratory at Patuxent, Maryland. With the identification number on the band, the Laboratory can match it with the place, date, age, sex and species of the bird as it was recorded when banded.

In times past, the communication was by mail. But these days the more timely—and reliable—means is by telephone. The finder may keep it; all that matters to the Laboratory at Patuxent is the knowledge of where the bird’s life story ended. As a thank-you, the recipient is sent a certificate with the information on the date, location and vital statistics of the bird when it was banded.

While the band is a trophy treasured by hunters, the real value in the process is the gold mine of information such bands have yielded to the Bird Banding Laboratory; information about the distribution, migratory paths and life span of the various waterfowl and other migratory bird species that are banded.

While most of the waterfowl band numbers reported are from birds harvested by hunters, some are not. According to author George Reiger in his excellent book The Wildfowler’s Quest, migratory bird bands have been found in such unexpected places as the stomach of a shark, in polar bear feces and embedded in the lip of a catfish! Though the number is now probably much larger, Reiger noted that there were more than 40 million records of banded migratory birds on file at the Laboratory in Patuxent when his book was published in 1989.

Among the more important results of this research is a gauge of how long some migratory birds can live. Some ducks harvested by hunters were over a decade old. The potential life expectancy of a goose can be measured in decades. Of course, the age of a hunter-harvested duck or goose is not a measure of how long it could live, since—by definition—it did not die of old age. Then again, it is the rarest of rare birds that dies of old age. Most wild creatures end their days in the talons or jaws of a predator; either when immature, in the prime of their life or in decline when their vigor has left them.

What Patuxent’s longevity findings suggest is that hunting mortality does make a difference in the abundance of ducks and geese. There is a wildlife management theory called “compensatory mortality,” which states that if a hunter did not harvest an animal, it would die of some other natural cause, like predation by a mink, a hawk or a fox. But when you discover that a bluebill can live seven years—as one banded bird harvested by Reiger did—you have to think twice. Few young ruffed grouse will survive to reach two years of age, and most brook trout live only about three. But band returns have told us that waterfowl can make the migratory journey time and time and time again. If a bird’s population status warrants harvest restraint, requiring it can make a difference.

The origins of bird banding are not found in America. In England, King Charles II and his successor James III in the mid-17th century banded waterfowl with silver or copper bands. But these were indicators of Crown ownership, not an interest in research. John James Audubon, the renowned naturalist and painter of bird life, is credited with attaching silver threads to the legs of songbirds, and thereby learning that they returned to the same place to breed.

But it was reformed market hunter Jack Miner in Ontario in 1909 who began the practice of banding waterfowl and recording the results of recovered metal bands. With the point of a pair of scissors he scratched his mailing address in a strip of aluminum that he bent around the leg of a black duck he captured. A hunter in South Carolina later shot it, and penned a letter to Miner to report the harvest. This revealed the migratory path and destination of the bird.

Today most waterfowl banding is done by state and federal agencies. But the object is the same: learn the birds’ life history secrets that only such stratagems can reveal.