BOSTON — Skies off Cape Cod are clouded with gulls; ponds around the country teem with troublesome carp, and trees in Florida bustle with Tarzan's monkeys. And it's all humanity's fault.
Just as neglect and excessive hunting have wiped out or endangered some species, putting animals into predator-free environments or giving them unlimited food supplies has resulted in animal population explosions.
Although experts say the pockets of overpopulation are not nearly as worrisome as the elimination of native creatures, they carry special concerns that often require action.
"Man has changed the environment to suit himself, and in most cases this has worked to the disadvantage of wildlife," said Sandy Sprunt, vice president for research at the National Audubon Society. "Now that we've created a problem, it's justified to do something about it."
Among the most drastic courses of action are sterilizing or killing overabundant species to prevent further disturbances to the ecosystem.
Poison is one method under consideration to control gulls on the Monomoy Islands, a 2,750-acre national refuge off Cape Cod that has the largest gull population in North America.
When the islands became a refuge in 1963, there were five pairs of nesting gulls. Fueled by a feast of garbage at the cape's landfills, which are growing with the region's population, the great black-backed and herring gulls now number 20,000 pairs.
The voracious gulls have squeezed out rare species of shore birds like piping plovers and roseate terns.
"Our desire is not to eliminate the gull colony," said Curt Laffin, chief of planning for the U.S. Fish and Wildlife Service's northeast office. "Our desire is to allow the full range of species that use the islands to nest."
A proposal calls for workers to mix the poison DRC 1339 with margarine, spread it on bread and drop pieces in the gulls' nests. Experience indicates that only the gulls will eat the bread, said Scott Melvin, zoologist for the Massachusetts Natural Heritage Program.
"It's manipulative wildlife management," he said, "but my feeling is that we're living in a very man-dominated ecosystem, and we're deluding ourselves if we think we can put a fence around this refuge and walk away and let nature take its course."
The main opposition has come from officials at the Massachusetts Audubon Society's Wellfleet Bay Sanctuary, who say they would prefer destruction of gull nests and eggs.
The Fish and Wildlife Service accepted comment through Jan, 9 on the plan, which also includes closing off nesting areas of threatened birds, barring dogs from the islands and requiring visitors to obtain permits.
Another human-created problem occurred at a Silver Springs, Fla., tourist attraction that was home to several hundred descendants of the wild rhesus monkeys used in Tarzan movies filmed there in the 1930s. The movies fell from fashion, but the monkeys kept multiplying.
In September, it was announced that 75 of the primates would be shipped to a Missouri animal farm. Some older females also were to be sterilized, with more to follow if no complications resulted.
The Florida Fish and Game Commission said the monkeys' wanderings posed a threat up to 60 miles away. There were 17 reports of monkey bites from 1977 to 1984.
Overpopulation also has been a problem with the common carp, a bottom-feeder introduced in the United States by the government in the 1800s.