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Mute Swans Make Noise:
Great Lakes Population
By Scott A. Petrie*
Introduction and Population
Mute Swans (Cygnus olor),
endemic to Eurasia, were introduced to North American city parks, zoos,
avicultural collections, and estates in the late 1800s and early 1900s.
The intentional releases and accidental escape of these birds and their
progeny resulted in a rapidly expanding free-flying feral population along
the northeastern Atlantic Coast of the United States, portions of the Pacific
Coast, and more recently, much of the southern half of the Great Lakes
basin. It is well known that exotic waterfowl can have negative ecological
impacts on native species, particularly if the introduced species is aggressive,
competes with other waterfowl for food or habitat, and/or hybridizes with
native species. Although hybridization is not currently a problem with
Mute Swans in North America, the species' size, extremely aggressive disposition,
and voracious appetite make it a strong competitor with substantial regional
impacts on native waterfowl and their habitats.
Populations of feral Mute
Swans in North America have been growing at an astounding rate. For example,
the Chesapeake Bay (Maryland and Virginia) populations have grown from
1962 when five birds were released, to approximately 4,500 birds last year.
Despite efforts to control them, the United States Atlantic Coast population
is close to 13,000 birds.
More recently (since the
mid-1960s), Mute Swans have been colonizing the Great Lakes watershed,
and the population is now nearly 10,000 birds. The southern Ontario population
is presently about 2,000 birds and is increasing at 10 to 15 percent per
year. At this growth rate, the southern Ontario population will double
every seven to eight years. Also, given that the lower Great Lakes includes
about 116,000 acres of coastal wetland habitat, the population could potentially
reach 30,000 swans. If Mute Swans populations increase to the point that
they begin nesting on inland wetlands and man-made waterbodies, as they
have in Poland and along the Atlantic Coast of the United States, we could
expect that the southern Ontario population could even surpass 30,000 birds.
The rapid growth rate of
southern Ontario's feral Mute Swans can probably be attributed to a number
of factors. The lower Great Lakes is climatically similar to the native
Eurasian range of Mute Swans. There are few natural predators of Mute Swan
nests, cygnets or adults on the Great Lakes. Mute Swans are dominant over
all other members of the lower Great Lakes waterfowl community. There has
been minimal interference with the birds by humans. In Ontario, these birds
have been protected under the Migratory Bird Act since 1974. Reduced availability
of lead artifacts in the environment has helped this species; Mute Swans
are highly susceptible to lead artifact ingestion. The recent warming trend
has been beneficial, as cold winters result in reduced overwinter survival
and future reproductive output. Finally, Mute Swans have large clutch sizes
and are capable of laying replacement clutches.
This rapidly growing Mute
Swan population is of concern for numerous reasons. Mute Swans are one
of the most aggressive species of waterfowl in the world; they regularly
attack other species of waterfowl, as well as other wetland-dependent birds.
They also are known to attack humans. Mute Swans maintain large territories
(>15 acres) during mating, nesting, brood rearing, and foraging; they have
even been reported to occupy territories throughout the year. During incubation
and brooding, cobs actively patrol the perimeter of their territory and
aggressively defend it, thereby forcing native species to nest and feed
in less-preferred areas.
displacing other waterfowl from their territories, Mute Swans reduce the
amount of staging and breeding habitat available to native species of ducks,
geese, and swans on the lower Great Lakes. This probably reduces the carrying
capacity of (with respect to number of birds and capability of birds to
acquire body fat) coastal wetlands for staging and breeding waterfowl.
Mute Swans have also been reported to kill ducks, Canada Geese, Pied-billed
Grebes, and herons, and cause nest abandonment in Least Terns, Black Skimmers,
Forster's Terns, and Common Terns. Therefore, as the quality and quantity
of wetland habitat continues to decline in North America, increasing populations
of aggressive Mute Swans serve to further reduce the carrying capacity
of remaining habitats for wintering, staging and breeding waterfowl as
well as other wetland dependent avifauna.
Competition in waterfowl
will most likely occur on wintering and/or spring staging areas where food
is most limiting. Whereas coastal Great Lakes wetlands are most important
as staging habitat for native waterfowl, these habitats are now being used
year round by Mute Swans. Being primarily herbivorous aquatic foragers,
Mute Swans consume daily at least six to eight pounds (wet weight) of submerged
aquatic plants, including leaves, stems, roots, stolons, and rhizomes.
Because adults also tend to paddle and rake the substrate to dislodge food
for themselves and their cygnets, additional vegetation is uprooted and
destroyed, further decreasing the availability of food for native waterfowl.
At high densities, Mute Swans can overgraze an area, causing a substantial
decline in the availability of submerged aquatic vegetation, before they
move to a new area. In extreme cases, Mute Swans can even eliminate some
plant species from an ecosystem.
Mute Swans increase their
feeding rate during spring and summer because more food is required before
feather molt and egg laying, which probably influences the availability
of submerged aquatic vegetation (SAV) to fall migrant waterfowl. During
winter, Mute Swans quite likely consume nutrient storage and overwintering
structures (tubers) that could have a long-term impact on aquatic plant
availability and species composition. For instance, perennial species such
as Vallisneria americana and Scirpus americanus overwinter as vegetative
buds, and the survival of these structures is the main determinant of the
next seasons growth. Therefore, feral Mute Swan populations reduce the
carrying capacity of lower Great Lakes wetlands for native waterfowl directly
via aggressive interactions (reduced space) as well as indirectly through
resource depletion (reduced food).
Given the similarity of climate
between Eurasia and North America, the unparalleled competitive abilities
of Mute Swans, and the almost total lack of predators, it seems highly
probable that Mute Swans will continue to increase exponentially in the
lower Great Lakes. As natural causes are unlikely to limit the population
in the near future, it seems prudent to control the species in the Great
Lakes region (and elsewhere) before the population becomes much larger.
The first step that should
be taken is to remove any legal protection for the species: this would
allow hunters and other private individuals to participate in control programs
without a need for special permits. Since 1974, in Canada, Mute Swans have
been on the list of bird species protected under the Migratory Birds Convention
Act, 1916, despite the fact that they are a nonnative species, and “Federal
law does not generally protect species or families that were introduced
to North America by humans, i.e., not native to this continent “ (Environment
Canada 1991). The species was originally listed in Canada as a means of
prohibiting releases of captive individuals. Its effectiveness for this
aspect is not known, but it has simultaneously had the effect of protecting
the species from hunting or harassment, thus allowing the population to
Control programs have been
implemented in a number of eastern U.S. states with varying degrees of
effectiveness. Rhode Island began a control program of egg addling and
pricking in 1979; despite the fact that 9,378 eggs were destroyed in 1,629
nests over a period of 22 years, the population increased by over 500 percent.
Vermont, in contrast, reported no Mute Swans in 2000, apparently as a result
of a lethal control program. This is supported by the fact that population
models indicate that the most effective way to reduce population growth
for a longlived species such as the Mute Swan is to reduce adult survival
rates. This could be done through capture and removal programs, or through
culling. Swan capture and removal during wing molt may be an appropriate
solution in some situations, but it is costly. It also is doubtful that
a sufficient number of repositories exist for these birds once removed
from the wild. Several hundred birds would have to be captured and removed
annually, and measures would have to be taken to ensure that captured birds
are never released back into the wild.
While the birds are not protected
under U.S. federal regulations and are unprotected in some states, other
states do protect the species, complicating the control issue.
A coalition of Mississippi
River flyway states will meet in February 2002 to review recommendations
for control of the birds. Joe Johnson, director of the Kellogg Bird Sanctuary,
part of Michigan State University's Kellogg Biological Station and chairman
of the Mississippi Flyway Technical Section Swan Committee, said, “We will
suggest that Mute Swan be accepted as an exotic species.” If Mute Swans
are accepted and regulated as exotic, then the states “should gain authority
over the sale and possession of Mute Swans and their eggs. And Mute Swans
captured as a result of citizen complaint should not be returned to the
wild.” The committee also will recommend that the U.S.Forest Service and
National Park Service should consider swan-management policies similar
to those of the U.S. Fish and Wildlife Service, which advised its managers
to take effective steps to protect lands under their jurisdiction from
degradation and destruction by Mute Swans.
Johnson said he would like
to see these states adopt a program similar to that of Minnesota, which
considers the species exotic, does not protect the birds, requires a permit
for ownership, and sets strict standards for control of captive birds.
The state presently has about 15 wild Mute Swans. Wisconsin also does not
protect the birds and requires a permit for ownership. Wisconsin, however,
has a Mute Swan population of about 600 birds. Both the number of swans
and the problems they cause conflict with native wildlife and public safety
are growing. Michigan, which does protect the birds, has the largest Midwest
population, about 4,000 birds.
In those jurisdictions where
Mute Swan populations have grown beyond novelty stage, Johnson said, “policy
should be to manage the population at a level that will have minimal impacts
on native wildlife or its habitat and on public safety.”
Therefore, a simple and effective
solution is to remove any protected status for the species, and encourage
hunters and managers of refuges and other waterfowl management areas to
control their numbers. If it was determined that these measures were not
sufficient, then professional culling programs could be implemented. Given
the present rate of increase, whatever control measures are selected should
be undertaken as soon as possible, before the population becomes too large
to control. However, Mute Swans are conspicuous, attractive birds that
appeal to many members of the general public, many of whom are unaware
of the swans' potential adverse ecological impacts. Attempts to control
this species in the U.S. have sometimes been thwarted by well-meaning,
but poorly informed citizens. Education and discretion must, therefore,
be an integral component of any well coordinated Mute Swan management program.
List of Resources
Here are a dozen key resources
for those birders who wish to pursue the subject.
Allin, C. G. 1981. Mute Swans
in the Atlantic Flyway. Proc. International Waterfowl Symposium. 4:149–154.
Allin, C. G., G. G. Chasko,
and T. P. Husband. 1987. Mute Swans in the Atlantic flyway: A review of
the history, population growth, and management needs. Trans. Northeast.
Sect. Wildl. Society 44:32-47.
Bellrose, F. C. 1980. Ducks,
Geese and Swans of North America. Stackpole Books, 540pp.
Ciaranca, M. A., C. C. Allin,
and G. S. Jones. 1997. Mute Swan (Cygnus olor). In The Birds of North America,
No. 273 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences,
Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.
Cobb, J. S., and M. M. Harlan.
1980. Mute Swan (Cygnus olor) feeding and territoriality affects diversity
and density of rooted aquatic vegetation. American Zool. 20:882.
Knapton, R. W. 1993. Population
status and reproductive biology of the Mute Swan, Cygnus olor, at Long
Point, Lake Erie, Ontario. Canadian Field Naturalist. 77:354-356.
Owen, M., and C.J. Cadbury.
1975. The ecology and mortality of Mute Swans at the Ouses Washes, England.
Petrie, S.A. 1998. Waterfowl
and Wetlands of Long Point Bay and Old Norfolk County: Present Conditions
and Future Options for Conservation. Report prepared for the Norfolk Land
Reese, J. G. 1975. Productivity
and management of feral Mute Swans in Chesapeake Bay. Journal of Wildlife
Weller, M. W. 1969. Potential
dangers of exotic waterfowl introductions. Wildfowl 20:55-58.
Wieloch, M. 1991. Population
trends of the Mute Swan Cygnus olor in the Palearctic. Wildfowl supplement
No. 1: 22-32.
Wilmore, S. B. 1974. Swans of
the World. Taplinger Publ. Co., New York.
Point Waterfowl and Wetlands
P.O. Box 160
Port Rowan, Ontario N0E
Site - http://www.bsc-eoc.org/lpbo/lpwwrf.html
is the Research Director of the Long Point Waterfowl and Wetlands Research
Fund. His work has focused primarily on the ecology of waterfowl in semi-arid
environments and the staging ecology of north-temperate-occurring waterfowl.