Mute Swans (Cygnus olor) Fact Sheet
What does a mute swan look like?
They are very large birds (25-30 lbs.) measuring 56-62 inches in length. Their orange bills with black knobs, white plumage and long necks make them conspicuous. When swimming, mute swans often hold their wings slightly upraised over their back, forming a hump if viewed from the side. Their young have a dusky tinge and grayish bill and usually remain with their parents for about four months.

Where are they found?
Mute swans reside primarily in estuarine river habitats with smaller numbers on inland lakes and ponds. The largest number of mute swans occurs in Talbot, Queen Anne, and Dorchester counties.

Where did mute swans come from?
Mute swans are not native to North America. They were brought to this country from Europe in the late 1800’s. Mute swans that escaped from captivity have established populations in a number of states. The mute swan population in Maryland originated from the escape of five captive birds in Talbot County in March 1962.

How many mute swans are there?
Currently, over 22,000 birds occupy coastal and freshwater habitats along the Atlantic coast from New Hampshire to Florida, the Great Lakes, Washington State, southern Ontario, and British Columbia. There are 3600 mute swans currently living in Maryland’s portion of the Chesapeake Bay. It is estimated that in ten years, if left unchecked there will be over 20,000 mute swans in the Chesapeake Bay region. Adverse ecological effects are occurring as a result of this swan population and will increase if the population is allowed to grow.

What do they eat?
A mute swan feeds almost exclusively on submerged aquatic vegetation or “SAV”, also referred to as Bay grass. Every day an adult mute swan eats eight pounds of SAV, year round. It is estimated that the 3,600 mute swans that reside in the Chesapeake Bay consume 10.5 million pounds of SAV each year, or about 10.5 percent of the total biomass of SAV in the Bay. In ten years, the estimated 20,000 birds would eat over 58-million pounds of Bay grass a year. Additional SAV losses occur through the mute swan’s foraging behavior – their consumption of immature seeds, removal of SAV biomass before plant maturation and uprooting of whole plants.

What harm does the mute swan do?
Mute Swans are voracious feeders on the Chesapeake’s wild grass beds, what scientists call “submerged aquatic vegetation” or “SAV”. Mute swans eat about eight pounds of it every day, which equates to approximately 10 million pounds of SAV consumed every year. This SAV is an important ecosystem in and of itself, as well as an important nursery area for the fish and crabs that are critical to the Chesapeake Bay estuary. SAV has declined throughout the Bay because of water quality problems, and the growing mute swan population is a threat to the native grass beds that remain.

The mute swan is one of the world’s most aggressive species of waterfowl. In Maryland, mute swan pairs have become a nuisance, driving people away from shorelines where swans vigorously defend their nest during the breeding season. This aggressive behavior has also led to the displacement of native birds from nesting and feeding areas. Mute swans are responsible for driving the last remaining colony of black skimmers, a state-threatened species, from the Maryland portion of the Chesapeake Bay. Mute swans have been observed exhibiting aggression toward tundra swans, driving them from their habitats of protected coves and feeding areas. Since the mid-1970s, Maryland's wintering tundra swan population has declined by about 30%.

Why doesn’t DNR relocate mute swans
to various breeders and individuals, both in and outside of Maryland?

The primary goal of the DNR Mute Swan Management Plan is to reduce the number of mute swans in order to protect critical Chesapeake Bay habitats. While the capture and relocation of swans to certain types of scientific or educational facilities is a strategy within the management plan, DNR has concluded that to allow swans to be “adopted” as pets would not only fail to solve the immediate problem, but may actually compound it.

All of the feral populations of mute swans in Maryland and other parts of the United States and Canada originated from either the intentional release or accidental escape of mute swans kept in captivity. In Maryland, all of our mute swans are the descendants of a single flock of five pet birds. Given the history of the species once it is introduced into captivity in new environments, it would clearly be irresponsible for us to relocate our swans to areas where they do not presently inhabit.

Every U.S. state wildlife management agency along the Atlantic coast and Canada has endorsed removal of adult swans. No state wildlife management agency wants or should allow the importation of this harmful species into their state. Nor would it be responsible for us to try to solve our problems by exporting them to adjacent states, either increasing existing populations or expanding the current range of the mute swan, which is already far too large.

Are there “good” swans too?
There are two species of swans that are native to the Chesapeake Bay that do not damage the aquatic ecosystem. One of these species, the trumpeter swan, no longer survives in the wild in this region. The other, the tundra swan, is only here in the winter months. Mute swans are not “bad” animals, they are just animals that have been introduced to an ecosystem in which their behavior and biology is a danger to the Chesapeake Bay ecosystem.

Have studies been completed on how best to deal with the mute swan?
The Swan Management Plan, released in April 2003, is a culmination of multi-year study by the Maryland Department of Natural Resources (DNR) of the impacts of the mute swan. The Plan provides direction and objectives for the Department to manage this overabundant species through 2008 including recommendations to reduce the current mute swan population. The overwhelming scientific evidence indicates that immediate, lethal action must be taken before mute swan populations continue to proliferate and irreversibly damage the Chesapeake Bay. The plan is available on line.

Do any other organizations support the Swan Management Plan?
The Plan has been supported and endorsed by local and national environmental groups; including the National Audubon Society, the Chesapeake Bay Foundation, the Severn River Association, the South River Federation, the American Bird Conservancy, the Wildlife Management Institute and numerous other organizations. These constituent groups recognize the benefits this plan will have on other species and the Chesapeake Bay as a whole.

Why do biologists believe it is necessary to kill mute swans?
Although non-lethal methods to control population growth will continue to be used, lethal control is necessary to reduce the population. The quickest–and most humane–way to effect a 67 percent reduction of the population is to decrease adult survivorship by killing adult birds. Because of the mute swan's high reproductive potential and long life spans, traditional alternative control methods–such as addling eggs to suppress recruitment of young–are not effective in reducing populations. Non-lethal techniques such as harassment, exclusionary devices, and behavioral modification generally have limited effectiveness and are suitable only for site-specific situations involving problem individuals or flocks.

Why can’t you just destroy the eggs or use birth control?
Wildlife Managers have been addling (preventing hatching of) mute swan eggs and this has slowed the rate of population growth. This practice will continue, however, egg addling alone will not lead to a significant reduction in swan numbers.

Using birth control on adult swans requires a surgical procedure, and it is simply impractical and too costly. Even if we used our entire budget for no other purpose, we could not capture and sterilize all of the mute swans.

Why can’t you capture the mute swan for re-locate them?
It is impractical to place the swans in zoos, parks, and retirement homes and DNR does not have the resources to capture, pinion, sterilize and find homes for hundreds, let alone thousands of these birds.

We cannot send them somewhere else either. Given the mute swan does not have a natural predator, they are overpopulating and damaging every area that they become established, in Europe as well as in North America. For example, in the Great Lakes area, mute swans are devouring native wild rice, destroying so much of this ethno botanically important plant that the Ottawa Nation has initiated a mute swan control effort.

What will happen if we don’t do anything about the Mute Swan?
Mute swans have a tremendous reproductive capacity and no natural predators. There were only 200 mute swans on the Chesapeake on the 1970’s. Without action, biologists believe that the current population of 3600 birds could exceed 20,000 in ten years. If this should happen, it may be impossible to restore SAV in the Chesapeake Bay. Native water birds and waterfowl would suffer, and the many aquatic species that depend upon the Bay’s wild grass beds to survive; crabs, seahorses, rockfish, and many more; would lose their homes.

Aren't mute swans legally protected in the United States?
Yes. Mute swans have been officially recognized as Federally protected in the U.S. since December 28, 2001. On that date, the U.S. Court of Appeals for the District of Columbia Circuit Court ruled that, as swans and members of the waterbird family Anatidae, mute swans were protected by the Migratory Bird Treaty Act. The MBTA provides strong measures for the protection and conservation of migratory birds, while at the same time providing opportunities for people to use the migratory bird resource for sport, recreation, and scientific endeavors. The MBTA also provides considerable flexibility for the U.S. Fish and Wildlife Service–the primary Federal agency responsible for migratory bird management–to implement actions to address situations in which birds may come into conflict with human interests, as in the case of mute swans. (http://migratorybirds.fws.gov/)

What management action is the Fish and Wildlife Service proposing for mute swans?
The Fish and Wildlife Service's preferred alternative is to adopt an integrated population management approach, which would authorize a suite of lethal and non-lethal methods to address a variety of problems caused by an increased abundance of mute swans. Lethal methods would include shooting with firearms and/or live-trapping followed by euthanasia, plus egg addling to reduce production of young. Non-lethal methods would include pinioning and sterilization, harassment, exclusion, behavioral modification, and capture and relocation. Most of these actions could be conducted only upon receipt of a depredation permit issued by the Fish and Wildlife Service. The goals will be to reduce existing populations and prevent further range expansion. (http://migratorybirds.fws.gov/)

Submerged Aquatic Vegetation (SAV)
& Mute Swans - Fact Sheet


What role does the Submerged Aquatic Vegetation (“SAV”) play in the Chesapeake Bay?
Grass beds are the basis of a complex web of life in the Chesapeake Bay and are essential to the health and survival of the Bay. It is the home of seahorses and pipefish, of crabs and juvenile fishes, of ducks and herons. The whole ecosystem needs this “nursery” in order to function.

Perhaps most important, SAV introduces life saving oxygen into the Bay. Just like with humans, underwater life needs oxygen to survive and Bay grasses provide this by taking in carbon dioxide and, in the presence of sunlight, releasing oxygen.

What are causes SAV depletion?
In the 1960s and 1970s, the SAV was damaged due to nutrient run-off and pollution. In the 1990s, the mute swans have reduced the availability of submerged aquatic vegetation, or SAV, to native wildlife, reducing recreational crabbing and fishing opportunities. Mute swans have been documented feeding on 23 species of SAV including 16 species of pondweeds – sometimes referred to as “grasses” – and seven species of algaes.

What is being done to increase SAV?
The Chesapeake Bay Program partners recently set a new SAV restoration acreage goal for the Bay of 185,000 acres by 2010 (about the size of Anne Arundel County). Without immediate action, this goal may be impossible to reach. http://www.dnr.state.md.us/wildlife/msfinalappendc.html

Additional Resources


Back to In Focus - Mute Swans
Posted August 8, 2003