For the Birds Radio Program: Eclipse Plumage (Date confirmed)

Original Air Date: July 19, 1989

Why do geese have a period when they can’t fly at all each summer?

Audio missing


Eclipse Plumage

(Recording of a Canada Goose)

Last week I got a call from listener Jude Collins who rubbed her binoculars in disbelief when she saw a Canada Goose ambling down Buffalo Street in Duluth. She wondered if it needed help, and what it was doing there.

I suspect that the bird was one of Duluth’s local geese—a flock can usually be seen from the high bridge swimming in the St. Louis River. This one probably got stranded away from water during a critical point in its summer molt.

Most birds lose one or two flight feathers at a time during their molt, and can continue flying as new feathers grow in. Watch adult crows flying in summer and early fall and you can often see the gap where a feather has dropped out. The wings are large enough, and the body light enough, that a crow missing one or two feathers per wing can stay aloft. But water birds like loons, ducks, geese, and swans have far heavier bodies relative to their wing size. Evolution has favored smaller wings to allow them to dive or dabble in water—larger, more buoyant wings would make it impossible to stay down, and they’d keep bobbing up like corks. But as the wings became smaller, they reached a critical point where now the birds can’t afford to lose more than a single feather without losing their ability to fly. So rather than making the molt even more dangerous by drawing it out, these water species concentrate the vulnerable period by losing all their flight feathers at once.

Loons, which can’t walk on land, stay in the water during their molt. But ducks, geese, and swans, which are excellent walkers, can leave the water if they feel like it, though they usually stay close to water to evade predators. I suspect that Jude’s goose had been flying around town when the critical feather became loose, and it suddenly found itself grounded. Even under the best of conditions geese spend a lot of time walking on land. The position and musculature of their legs makes them well adapted for long-distance hikes, and so the one she spotted should be just fine, assuming people and dogs leave it alone. It was last seen headed for the lake, and with luck it should be back with its friends in the bay by now.

Wildlife biologists take advantage of waterfowl’s flightless period to conduct goose roundups in order to band geese. Although the geese can easily outrun and out-maneuver a single person, by setting up nets or walls and using several people at once, it isn’t too difficult to trap most of a flock for banding and study. Of all bird bands, the rings on waterfowl are the most likely to be recovered when the bird dies, since they are the birds most likely to be killed by hunters. Sending these bands to the U.S. Fish and Wildlife Service provides valuable information about migration and longevity. For example, the band on one Green-winged Teal found by a hunter established that the individual had lived for 20 years. Obviously most of the ducks and geese killed by hunters are younger and less experienced, but there have been band returns for Canada Geese that were 12, 18, and 23 years old.

Most bird deaths take place in summer and early fall. Birds can’t read those little lawn flags warning of toxic chemicals, cats are out in full force, and inexperienced baby birds are crashing into windows, power lines, transmission towers, and all sorts of things their natural instincts never warned them about. But I sure hope that one lone Canada Goose walking through Duluth makes it to the harbor safely.

(Recording of a Canada Goose)

This is Laura Erickson, and this program has been “For the Birds.”