Recent Arrivals to the Urban Scene

Compared with squirrels and raccoons, the beaver is a relative latecomer to populated areas. But the beaver population has been surging in the 1990's, mainly in fringe and suburban habitats. Fairly typical is the situation across central Maine. There, beavers are gnawing down trees and damming streams in residential suburbs and occasionally even in downtown Augusta, the state capital. The beaver population explosion in Maine stems from two causes, according to biologist Gene Dumont of the state's Department of Inland Fisheries and Wildlife. First, from the 1930's onward, many farmers abandoned the land, and their farms reverted to forests crisscrossed by streams—the perfect habitat for beavers. Then, in the 1980's, the demand for beaver pelts in the clothing industry started to decline, pelt prices dropped, and the number of trappers fell by half. By 1996, Maine's beavers numbered in the tens of thousands.

Known as the engineers of the animal kingdom, beavers build dams to create ponds, and within the ponds they erect cone-shaped lodges out of logs, stones, and mud where they live and raise their young. But beavers do not restrict their dam-building to streams in forests. Beavers have found it far easier to plug a drainage culvert 1 meter (3 feet) wide under a road than to build a dam 90 meters (100 yards) wide across a stream. Water backs up behind the plugged drains, flooding the landscape and washing out roads.

Wildlife officials have tried relocating beavers, but the animals return or others move in. Moreover, once caught and released, a beaver learns to avoid traps. A new strategy calls for clearing the debris from a culvert, fencing it off, and building a half-moon-shaped structure of metal posts and fencing upstream from the drain. Once the beavers build their dam against the barrier, officials insert drainage pipes to allow water to flow through the dam to the drain.