for National Geographic News
Bathing mute swan eggs in vegetable oil may sound like an old Eastern Shore recipe from Maryland's Chesapeake Bay region. Instead, it's a form of egg addling, a method used by wildlife managers to prevent the non- native birds from reproducing.
Although strikingly elegant, mute swans (Cygnus olor) are one of the bay's most harmful species, edging out native waterfowl and destroying aquatic vegetation. Egg addling has slowed the species' population growth, but not quickly enough to protect the bay's already fragile resources.
Seeking more drastic cuts in the bird's population, the Maryland Department of Natural Resources (DNR) unveiled a plan in April to shoot 1,500 mute swans. But one animal-rights group, the New York City-based Fund for Animals, denounced the plan and filed a lawsuit, prompting the DNR to suspend its plan pending further review.
Meanwhile, the birds continue to reproduce.
Explosive Growth
Mute swans, native to Europe and Asia, are found throughout the Chesapeake Bay and its major tributaries. The invasive species first took roost in the area when five birds escaped from captivity in 1962. Since then, the population has grown to 3,600 birds, having reached an all-time high of 4,000 birds in 1999.
"In 40 years this population has doubled more than nine times," said Jonathan McKnight, associate director of habitat conservation for DNR. "We've got a bunch of birds that are ready to start nesting this year or next, and it is clear that the population could reach 20,000 birds in 10 years."
While their name sounds serene, mute swans are ruthless competitors for food. Each year, the swans eat an estimated 10.5 million pounds (4,800 metric tons) of underwater aquatic vegetation, primarily grasses, according to DNR officials. Aquatic vegetation improves water quality and provides essential habitat for waterfowl, fish, and shellfish.
The birds are also aggressively territorial. Mutes have trampled nests of least terns (Sterna antillarum) and black skimmers (Rynchops niger) and driven off tundra swans (Cygnus columbianus), black ducks (Anas rubripes), and other birds from feeding and roosting areas.
Officials from the Commonwealth of Virginia, which shares a border with Maryland along the Chesapeake Bay, have also studied the swans and developed vegetation restoration programs. Unlike Maryland, Virginia allows hunting of the swans. But because the swans are protected under Maryland state law, this issue has mainly been Maryland's albatross.
Stemming the Baby Boom
DNR's mute swan management plan also called for non-lethal population control methods, such as egg addling and relocating birds from sensitive areas. The plan was endorsed by several environmental groups, including the local Chesapeake Bay Foundation in Annapolis, the National Audubon Society in New York, and the American Bird Conservancy in The Plains, Virginia.
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