Exotic Mute Swans Continue Population Increase

Maryland Department of Natural Resources Waterfowl Program Manager Larry Hindman has announced the results of the 1999 aerial mute swan survey. The total number of mute swans counted was 3,955, a 46% increase over the 2,700 swans counted during the 1996 survey. The 1999 mute swan population included 594 breeding pairs, 2,715 nonbreeders, and 646 young (called cygnets). Conducted every three years throughout the Atlantic flyway, the aerial survey of the Maryland portion of Chesapeake Bay was conducted by DNR Wildlife and Heritage Division staff between Aug. 18 and Sept. 9.

Mute swans, native to Europe and Asia, were transported to North America in the late nineteenth century by European immigrants. Some swans eventually escaped or were deliberately released into the wild. In Maryland, the mute swan population has become established from the original escape of five captive swans in 1962.

Swans (native, wintering tundra swans and exotic mute swans) in Maryland are classified as "wetland game birds." Thus, mute swans are protected by State law. Mute swans, however, are not listed as a migratory bird by the federal Migratory Bird Treaty Act. Therefore mute swans are not federally protected.

Mute swans reside primarily in estuarine river habitats with smaller numbers on inland lakes and ponds. The largest number of mute swans occurs in the lower Chester River south to the Little Choptank River along the Eastern Shore. Lesser numbers of mute swans were observed in lower Eastern Shore tributaries, with local concentrations in the vicinity of Hoopers and Bloodsworth Islands, and Western Shore tributaries, like the Patuxent River.

Public opinion about mute swans is mixed. They are very large birds, measuring 56-62 inches in length. With little or no fear of humans, they are easily observed and provide opportunities fro people to come in close contact with wildlife. However, the population growth and range expansion of this species has increased the number of swan-related problems, particularly for native wildlife and people.

Since mute swans did not evolve with native Bay wildlife species, problems for native wildlife have occurred. In the early 1990s, a large molting flock of more than 600 mute swans caused a colony of least terns and black skimmers (both State-threatened species) to abandon their nesting site on Barren Island in Dorchester County. This was the only skimmer nesting colony in the Maryland portion of Chesapeake Bay. These swans also displaced nesting Forster's and common terns, declining species in Maryland. In other areas of the state, mute swans have also been documented killing mallard ducklings and Canada goose goslings.

A major concern is the effect of interspecific competition between mute and tundra swans. Mute swans have been observed exhibiting aggression toward tundra swans driving them from protected coves and feeding areas, important habitats for native tundra swans. Since the Mid-1970's, Maryland's wintering tundra swan population has declined by about 30%. However, research is needed to tell if this decline is related to increased competition from mute swans.

Mute swans feed almost exclusively on SAV (submerged aquatic vegetarian) like widgeon grass and redhead grass. Citizens frequently complain that mute swans reduce the availability of SAV to native wildlife, reducing recreational crabbing and fishing opportunities. Concentrations of mute swans have over-grazed bay grasses, eliminating habitats for crabs, fish, and other wetland dependent species. Loss of important Bay grasses and valuable habitats in some localities has been severe.

Some mute swans are aggressive and will attack humans, especially small children, in defense of their nest territory and young cygnets. Although the potential for injury is very low, their territorial behavior is a nuisance and renders some land or water areas inaccessible to people during the nesting and brood-rearing season.

In the absence of population control measures, it is expected that the number of mute swans in Maryland will continue to increase. Eventually, this exotic species could occur throughout the Chesapeake Bay region and cause additional ecological harm and problems for humans. In response to public interest, the Department of Natural Resources has appointed a citizens advisory committee to identify pubic concerns and suggested strategies related to the management of mute swans in Maryland.

Posted: 3-17-2000