SAV estuary

Background

The mute swan (Cygnus olar) was introduced to the Chesapeake Bay region for its ornamental value but has had an increasingly disruptive effect on the ecology of the Bay as well as on that of other areas as far north as Maine and as far west as Michigan. The mute swan was first introduced to North America in the 19th century in the Hudson River Valley region of New York from Europe and Asia. Mute swans live primarily in estuarine river habitats, with smaller numbers occurring on inland lakes and ponds.

Mature mute swans are larger than the Chesapeake Bay's native tundra swans; they may become as heavy as 25 pounds versus16 pounds. They are also very aggressive. Mute swan cobs (males) have been known to protect up to a six-acre area surrounding their nests in ponds, lakes and marshes. A mating pair of mute swans will return for many years to their established territory, and often will remain throughout the year near the Chesapeake Bay.

The Problem

There appears to be interspecific competition between mute swans and our native tundra swan which winters in the Chesapeake Bay, but breeds in Alaska and Canada. Mute swans have been observed exhibiting aggression toward tundra swans, driving them from protected coves and feeding areas. The mute swan may be responsible for recent declines in tundra swans wintering in the Chesapeake Bay, but studies are needed.

Mute swans are estimated to eat over 9,000,000 pounds of submerged aquatic vegetation (SAV) each year. The loss of SAV, plus the damage to the beds is limiting the recovery of SAV which provides food and habitat for Bay organisms. Mute swans threaten biodiversity by trampling eggs and chicks of nesting native waterbirds, such as the threatened black skimmer and terns.

The Solution

The mute swan population in the Chesapeake Bay area has grown by over 1,150 percent since 1986. Chesapeake Bay mute swan population has soared in recent years; in 2002, 4,156 swans were counted - a tremendous increase over the 264 recorded in 1986. While this population may sound manageable, especially when compared with the populations of other invasive species, the swan's aggressive territorial behavior and destruction of SAV beds make even a small population of these birds a potentially serious threat to the Bay's sensitive ecosystem. Since the mid-1990s Maryland DNR and some Federal agencies have attempted to control mute swan populations by addling eggs to prevent further spread. Since the population has continued to grow, Maryland has decided to remove birds in addition to addling eggs in order to reduce the population. Mute swan control activities are coupled with outreach activities to heighten public awareness of the problems created by mute swans.

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Last modified: 04/24/2003