Amazing what you can learn from a 5-cent metal band on a bird’s ankle.

Climb a pine tree to a bald eagle’s nest in Beltrami County in 1977, clamp a numbered band around the ankle of an eagle chick, and when that eagle shows up dead in New York — in 2015 — you now know that the nation’s symbol can live at least 38 years in the wild.

Related Articles 7 things we’ve learned from a century of tagging Minnesota birds That’s a true story, like countless others being recalled this week as birders, biologists, hunters and others begin a year-long observation of the 100th anniversary of the North American Migratory Bird Treaty. The centennial was front-and-center Saturday at the Minnesota Waterfowl Symposium in Bloomington and earlier in the week at the North American Duck Symposium in Annapolis, Md.

The 1916 treaty between the United States and Great Britain (acting on behalf of the “Dominion of Canada”), was among the legal pillars for modern conservation, establishing that what would become more than 800 species of birds existed for non-commercial uses and needed protection to ensure their survival forever.

Much of that lofty aim could not have been accomplished without understanding the birds themselves: where they live, for how long, how many there are, how often they reproduce, and so on.

And the answers to those questions would not have been possible without the North American Bird Banding Program, which was essentially established as a result of the treaty.

From understanding the bar-tailed godwit’s 7,000-mile non-stop flight between Alaska and New Zealand to establishing that spent lead ammunition was poisoning waterfowl, data gleaned from bird banding has inspired wonder, informed policy and helped protect untold numbers of birds from habitat destruction or overhunting. Hunting regulations for ducks, geese, cranes and doves owe their promise to kill at sustainable levels to the banding program.

The program is simple: Using uniquely numbered bands, identify birds — lots of them — and wait for the public to tell you every time that bird shows up somewhere.

It only works if you band lots of birds. Each year, an average of 1.2 million birds, from trumpeter swans to hummingbirds, are banded, with the Bird Banding Laboratory in Patuxent, Md., receiving some 87,000 reports annually of bands being spotted.

Usually, the birds are dead. In a phenomenon that might make some non-hunting bird lovers uncomfortable, migratory game birds such as ducks and geese are among the best-monitored populations — because hunters blast them from the sky with shotguns and report any banded birds to the lab at a rate of 80 percent. Crucial knowledge of migration patterns learned last century was the direct result of duck hunters.

“The whole concept of flyways came about after waterfowl were banded starting in the 1920s,” said Bruce Peterjohn, chief of the Bird Banding Lab, which is run by the U.S. Geological Survey. “When there were finally enough records of banded birds coming back from hunters, it became clear that these birds were following established routes year after year. That’s how we know that.”

For Canada geese and mallard ducks, between 6 percent and 10 percent of the bands affixed to birds end up being recovered, Peterjohn said. “For non-game birds, the number is much less. Large birds like bald eagles are more likely to be spotted if one dies, but when you get down to songbirds, it can be one return for every 10,000 banded,” he said. “There are a few birds where we’ve banded maybe 4,000 or 5,000 a year for 50 years and only have a dozen records. That doesn’t tell you a lot.”

But technology is changing that. With a general population packing digital cameras in their smartphones, and birders carrying cameras with powerful lenses and sensors, the lab is increasingly receiving reports of banded birds flying unharmed via 800-327-BAND or ReportBand.gov. For example, hummingbirds have been banded for about 20 years, but only recently has the lab begun to see decent numbers of returns, and many are by amateur photographers shooting pictures of hummingbirds at their homes’ feeders, and then enlarging the image to read the band info.

But in an era of drone surveillance, global positioning satellite trackers and ingestible pills that can monitor an animal’s heart rate, how can it be that a simple metal band, which cost between a nickel and a quarter each, still has a place?

“That’s a really good question,” Peterjohn said. “Technology is changing the nature of the bird banding program. A GPS tracker can provide a lot more information on day-to-day bird movements than a metal band that you hope someone will report years later.”

But such devices are still too large for many birds, and their batteries only last a few years, while many birds, bands have taught us, live decades.

“We haven’t created high-tech systems that can do that yet, and then there’s the cost. You’re talking thousands of dollars each for GPS. A metal band only costs a few cents, and they mark most birds for life.”