The U.S. Fish and Wildlife Service has approved a Maryland program to “addle” mute swan eggs to help slow the population growth of the foreign waterfowl.

The Service approved a plan from the Maryland Department of Natural Resources to spray vegetable oil on eggs in up to 350 nests in the state, which kills the embryos inside.

The service also approved a program proposed by the National Capital Park and Planning Commission to control mute swans on federal lands in and around Washington, D.C.

Efforts to control the region’s mute swan populations had been put on hold by a U.S. Court of Appeals for the District of Columbia ruling in

December that the mute swan is covered by the Migratory Bird Treaty Act, even though it is not a native species.

In its ruling, the court noted that the act specifically protects “wild ducks, geese and swans.” Although the mute swan may be a nonnative, it was clearly a swan and therefore protected by the act, the court said.

Originally, it was thought that the court ruling would halt any efforts to control mute swans for this year. But after reviewing the ruling, federal officials decided they still had authority to issue permits for actions that would limit damage by the swans.

Mute swans are native to Europe and Asia, but were brought to North America in the late 1800s to adorn ponds. In the early 1960s, five swans escaped and took up residence on the Bay.

The swans have no natural predators around the Bay, allowing their population to mushroom to about 4,000, mostly in Maryland, and biologists believe that number could double as early as next year.

Also, the birds do not migrate and therefore feed on the Bay’s valuable underwater grass beds during the critical summer growing season, when most

other waterfowl are gone. Biologists estimate the swans eat about 9 million pounds of underwater grass beds annually, and they say flocks of swans can eliminate grass beds from some areas.

In addition, flocks of mute swans have overrun the nesting sites of least terns and skimmers, both rare species in the region, squashing their eggs and killing the young. As a result, state and federal biologists have taken to addling mute swan eggs on state and federal lands so they will not hatch.

A special Maryland task force has been developing a strategy to control the swans. Early versions of its strategy called for designating “swan-free zones” around sensitive resources where troublesome birds could be shot as a last resort. The strategy has not been finalized, but is expected to be completed later this year.