In the last column, I described the techniques bird banders use to safely capture and fit birds with uniquely numbered aluminum bands. The Bird Banding Lab, a federal office, serves as the central repository for all banded birds. The data includes all recaptures or recoveries of banded birds.

The first banding of birds we know of was done by John James Audubon in eastern Pennsylvania. He tied some aluminum wire to some nesting eastern phoebes and found that the birds returned the following year to nest. By marking the birds, he was able to demonstrate that these birds are faithful to their nesting sites over the years.

Of course, the power of modern bird banding depends on banded birds being subsequently caught or found dead so the band number can be read. Knowing when the bird was banded provides information on the spatial movement of the bird as well as its minimum age.

The success of any banding program hinges on the rate at which banded birds are re-encountered. The chances of capturing a banded bird are obviously greater for resident birds. For migratory birds like shorebirds, warblers and many other birds, few banded birds will be re-encountered. But there are thousands of banded birds so at least a few are subsequently encountered by banders elsewhere.

For larger birds like geese or eagles, the band number can often be read directly with a spotting scope so such birds need not be recaptured to identify the individual.

Many banders now place color bands, in addition to the required aluminum bands, on captured birds. Color banding requires special permission from the Bird Banding Lab to ensure that banders in the same area are not duplicating banding combinations. By using a unique combination of color bands for each bird, one can identify individual birds without having to recapture them to read the band number. I used this technique to study the variation in visitation of feeders in black-capped chickadees and to gauge the stop-over duration of western sandpipers in Washington state.

The Pan American Shorebird Program has instituted a valuable protocol followed by shorebird banders in North America. Banders fit captured birds with a standard numbered aluminum band and a plastic color band with an extension perpendicular to the shorebird’s leg. These elongated bands are appropriately called flags. Each region in the Americas has a unique color. Banders use white flags in Canada, green flags in the U.S., grey flags in Central America, pink flags in the Caribbean and so on.

The extension on the color band makes the flag easy to see through a spotting scope. One does not know the specific identity of a flagged shorebird without capturing it but if you see a shorebird with a red flag, you know it was banded in Chile. That is valuable information.

The millions of banding records and the thousands of recapture records are available to interested researchers. This database has been a boon to me in my studies of irruptions of finches and red-breasted nuthatches.

Here are a few of the ornithological discoveries that have been made possible by banding birds. Re-encounters of banded Arctic terns show they migrate from pole to pole, twice a year.

By following the disappearance of resident banded birds (presumably because they died), we know that many resident songbirds have a 50% chance of dying every year. So how about a chickadee banded in Minnesota that was recaptured 11.5 years later! That’s a ripe old age for a species where few even live to see a fourth birthday.

We have learned much about where different populations of birds winter. For instance, palm warblers do an interesting crisscross in migration. Populations breeding in the upper Midwest and the prairie provinces of Canada migrate southeast to winter in Florida while our eastern palm warblers migrate southwest to winter along the Gulf Coast.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu