Trumpeter swans change their tune. Northwest swans alter feeding habits, grow healthier as result
Louis, the voiceless swan in E.B. White's children's classic, adapted to his problem in an unusual way - he learned to communicate by blowing into a trumpet. The trumpeter swans in the Skagit Valley, the major wintering grounds in the Northwest United States, have learned a few things, too - so one theory goes.
Mike Davison, a regional biologist at the Washington State Department of Game, says he has noticed significant changes in the feeding, wintering, and social habits of the swans. Some experts theorize that the trumpeters have picked up these habits from socializing with another type of swan, the tundra (formerly called whistling) swan. In any case, the changes are resulting in healthier trumpeter swans, says Mr. Davison.
There has been a dramatic increase in the number of trumpeters in the Skagit Valley over the last 20-odd years. In 1963, when swans were first spotted in the valley, 23 were counted. Last November, the state department of game counted 473.
This patterns an increase in the trumpeter population as a whole. Back in the '30s, the birds were on the edge of extinction, with a 1932 census counting only 69 swans throughout North America. Swan management programs, undertaken by the US and Canadian game departments, have brought the North American population back to an estimated 11,000 birds.
The valley's wintering trumpeters begin appearing in early November, riding in on advancing weather fronts. They remain until early spring, and by the second half of March they have returned to their breeding grounds on the Kenai Peninsula in south-central Alaska and the Alaskan and Canadian Arctic.
A change in swan feeding habits is described by Winston E. Banko, a local swan expert.
``Historically trumpeters have been grazers, feeding on pasture lands and aquatic plants. Over the past six or seven years they have switched to eating corn almost to the total exclusion of grass.'' This change, says Mr. Banko, is unique to the swans in the Skagit Valley.
The leading theory explaining the switch to corn feeding is tied to a change in the birds' social structure. Trumpeters and tundra swans are cousins. In the past, they have inhabited separate feeding and resting areas in the valley. But during the last half dozen years or so, the two species have been feeding together a fair amount of the time. Some experts suggest that the trumpeters have learned corn eating from the tundras.
The change in the swans' diet has resulted in healthier birds, according to swan experts. To ensure an adequate supply of corn, Washington State Department of Game officials are setting up a program with area farmers to grow corn and barley, and to leave these grains unharvested in the fields as food for the swans during their winter stay. But as of yet, the full effect of the mingling of the two species has not been documented except for increased sociability among the swans.