Development makes songbirds easy prey.

Loss of North American forests may explain, at least in part, the "alarming" decline in migrating songbirds, researchers report in the fall ECOLOGY AND CONSERVATION OF NEOTROPICAL MIGRANT LANDBIRDS.

By some estimates, songbirds that summer in North America and winter in the tropics have experienced population declines of 3 percent each year since the late 1970s. to get to the root of the problem, Richard T. Holmes of Dartmouth College in Hanover, N.H., and Thomas W. Sherry of Tulane University in New Orleans studied a population of American redstarts (Setophaga ruticilla) that summer in New Hampshire's White Mountains and winter in Jamaica.

The 10-year study revealed a strong statistical correlation between fledgling survival in summer and population changes the following year. Rather than dying in Jamaica or during the long migrations, the young warblers appeared to face their greatest risk in North America. While many factors affect fledgling survival, this study indicates that North American predators pose the greatest threat, the investigators say.

Although some researchers have blamed deforestration in Central American and the Caribbean for the birds' population bust, the redstart findings provide the strongest evidence yet that North American land-use patterns contribute to this decline, Holmes contends. As trees fall under the developer's ax, predators venture farther into the forest interior, thereby putting more fledglings at risk, he explains. Even in New Hampshire, where forests remain relatively intact, says Holmes, predation appears to be the key factor in redstart population size. Thus, he suggests, its effect may be even more pronounced in heavily deforested regions of North America.