Nov 05 2009
Tundra swans are on the move.
Last Sunday at the Allegheny Front we heard three flocks whoo-ing overhead before we saw them very high above us, heading southeast to the Chesapeake. That night I heard another flock pass over my house though I couldn’t see them in the dark. As their voices faded in the distance I heard a lone swan following them. He had fallen behind.
Swans and geese fly in V formation because it cuts down on wind resistance. The lead bird takes the brunt of the wind and expends the most energy. The birds who follow fly just above the wing of the bird ahead of them and ride a cushion of air created by the previous bird’s wing. Eventually the lead bird tires, falls back in the flock and lets another bird take the point position. In this way the entire flock shares the burden and is able to fly further without becoming exhausted.
A lone bird gets no benefit from the V formation and, if he’s trying to rejoin the flock, he must fly faster than they do. If they don’t slow down, how can he ever catch up?
Tundra swans travel in family groups and pause more often during fall migration so their young can regain energy and keep up with the flock. Juvenile swans are especially vulnerable if they fall behind because they don’t know the migration route. They learn it from their elders on their first trip south. If a juvenile becomes separated from the flock, he’s lost.
It’s poignant to see a lone juvenile tundra swan in November. When I do I always hope another flock will come along to take him in.
(photo by Steve Gosser)
(p.s. How to recognize juvenile tundra swans: In this picture there are three adults and four juveniles. The adults have bright white heads, the juveniles have grey heads that gradually lighten to white on their necks. Sometimes the juveniles have pink on their bills.)