SOLVING THE SONGBIRD ENIGMA

It is one of the environment's most poignant mysteries: for some as yet unknown reason, migratory songbirds appear to be declining in many parts of North America. Some researchers put the blame on the destruction of tropical forests, where most of the birds spend the winter. Other scientists think the main cause lies here, in the forests of North America, which are becoming increasingly suburbanized and fragmented.

After 20 years' research at the Hubbard Brook experimental forest in the White Mountains, Dartmouth ecologists Richard Holmes and Thomas Sherry are leaning toward the second theory. They have found that songbird populations in the stillwild forests of the White Mountains are holding their own. Advocates of tropical deforestation as the cause of declines "may be using third-world countries as scapegoats for our own environmental problems," says Sherry. With a grant from the National Science Foundation, the two scientists plan to follow the birds south to Jamaica so they can study the effects of wintering, as well as breeding, conditions on migratory songbird populations.

Why are migratory birds dying? College ecologists have a suspect.