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Mute
swans
Mute
swans are native to Europe and Asia and only arrived in
North America during the late nineteenth century. After
being imported by European immigrants, a few birds either
escaped or were released into the wild. In 1962, five
swans escaped from a pen near St. Michaels and started
the Maryland population. Since then, their population
has exploded.
Picture:
Mute swans with eight cygnets. The
orange bills distinguish the non-native mute swans from
the native tundra swans that have black bills. Picture
courtesy of Mary Hollinger, NODC biologist, NOAA. 
To
the original photo.
It
is important to note that mute swans are doing nothing
more than being mute swans in the wild. The problem is
that they are an invasive species, so native species have
not evolved defense strategies against these prolific
birds. With no natural predators, their population remains
completely unchecked and therefore unbalanced. This has
happened with other species in the Chesapeake Bay watershed,
species such as the reed grass phragmites, the Asian
long-horned beetle, and the oyster parasite MSX.
With
that said, it is still true that mute swans are large,
aggressive birds who actively defend their territory,
and this means trouble for some native species. Mutes
have driven out colonies, in some cases the last colony,
of black ducks, black skimmers, and least terns. Of major
concern as well is the competition between mute swans
and tundra swans. While tundra swans have been present
in the Bay area for several millennia and are considered
a native species, mute swans have only been here for several
decades, which is why they are considered non-native or
invasive. Mute swans have driven tundra swans out of important
feeding areas and since the 1970's the tundra swan population
has decreased by 30%. Many have rushed to blame this decline
on the mute swans, but researchers have not yet established
a direct link.
Picture:
A flight of black skimmers. The
habitat of the black skimmers is threatened by the mute
swans. Picture courtesy of NOAA. To
the original photo.
The
differences between mute swans and tundra swans is telling
for the problems invasive species, like the mute swan,
can cause. Tundra swans migrate to the Bay for the winter
after breeding and nesting along the Arctic coast from
the Hudson Bay to the Bering Strait. Because they are
only around the Chesapeake Bay during the winter, they
consume far less submerged aquatic vegetation (SAV) then
do the mute swans who are at the Bay all year round. Because
tundra swans only eat SAV in the winter, the plants have
had a chance to mature and drop their seeds. Not only
do mute swans eat more SAV, they eat it during the plants'
delicate growing season. The birds are different in appearance
as well; mute swans are much larger (30 lbs vs. 15 lbs)
and have an orange bill instead of a black one.
Since
the mid-1990s, the Maryland Department of Natural Resources
(DNR), along with some federal agencies, has taken active
steps to control mute swans and prevent them from becoming
established on lands managed by DNR. Control has included
the prevention of eggs hatching, live capture and removal
of adult swans, and humane euthanasia of adult swans.
DNR has also authorized landowners to control mute swans
that are causing either a nuisance or property damage.
These activities have been combined with efforts to increase
public awareness of the problems caused by mute swans.
In 1998, Governor Glendening of Maryland appointed a committee
to develop mute swan management recommendations. These
recommendations are expected to be a combination of lethal
and non-lethal methods designed to reduce the mute swan
population to a level that is compatible with native wildlife
and creates less conflict with humans.
References
and further reading
Stemming
the white tide of mute swans.
Information from the Chesapeake Bay Foundation.
Exotic
mute swans continue population increase.
Article in TheChesapeakeBay.com.
Mute
swans: Beautiful but controversial birds.
Information about the mute swan by Larry J. Hindman, Waterfowl
Project Manager for the Maryland DNR Wildlife and Heritage
Division. The website includes a graph that shows how
the mute swan population has exploded in the past years.
Summary
of information by the Maryland DNR Mute Swan Task Force.
Information about population status, impacts on native
wildlife and people, and management needs in Maryland.
(January
2001.)
Protection
of mute swans ordered by federal court.
Article in SunSpot.net on January 3, 2002.
Several
other Watershed Radio programs feature invasive
or non-native species.
