Mute Swans Make Noise: Lower Great Lakes Population Scrutinized
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Mute Swans Make Noise: Lower Great Lakes Population Scrutinized Scott A. Petrie* Introduction and 10 to15 percent per year. At this growth Population Status rate, the southern Ontario population Mute Swans (Cygnus olor), endemic to will double every seven to eight years. Eurasia, were introduced to North Also, given that the lower Great Lakes American city parks, zoos, avicultural includes about 116,000 acres of coastal collections, and estates in the late 1800s wetland habitat, the population could and early 1900s. The intentional releas- potentially reach 30,000 swans. If Mute es and accidental escape of these birds Swans populations increase to the point and their progeny resulted in a rapidly that they begin nesting on inland wet- expanding free-flying feral population lands and man-made waterbodies, as along the northeastern Atlantic Coast of they have in Poland and along the the United States, portions of the Pacific Atlantic Coast of the United States, we Coast, and more recently, much of the could expect that the southern Ontario southern half of the Great Lakes basin. population could even surpass 30,000 It is well known that exotic waterfowl birds. can have negative ecological impacts on The rapid growth rate of southern native species, particularly if the intro- Ontario’s feral Mute Swans can probably duced species is aggressive, competes be attributed to a number of factors. with other waterfowl for food or habi- The lower Great Lakes is climatically tat, and/or hybridizes with native similar to the native Eurasian range of species. Although hybridization is not Mute Swans. There are few natural currently a problem with Mute Swans predators of Mute Swan nests, cygnets in North America, the species’ size, or adults on the Great Lakes. Mute extremely aggressive disposition, and Swans are dominant over all other voracious appetite make it a strong members of the lower Great Lakes competitor with substantial regional waterfowl community. There has been impacts on native waterfowl and their minimal interference with the birds by habitats. humans. In Ontario, these birds have Populations of feral Mute Swans in been protected under the Migratory North America have been growing at an Bird Act since 1974. Reduced availabili- astounding rate. For example, the ty of lead artifacts in the environment Chesapeake Bay (Maryland and has helped this species; Mute Swans are Virginia) populations have grown from highly susceptible to lead artifact inges- *Research Director 1962 when five birds were released, to tion. The recent warming trend has Long Point Waterfowl and Wetlands approximately 4,500 birds last year. been beneficial, as cold winters result in Research Fund Despite efforts to control them, the reduced overwinter survival and future P.O. Box 160 United States Atlantic Coast population reproductive output. Finally, Mute Port Rowan, Ontario N0E 1M0 is close to 13,000 birds. Swans have large clutch sizes and are [email protected] More recently (since the mid-1960s), capable of laying replacement clutches. SAP is the Research Director of the Long Mute Swans have been colonizing the Point Waterfowl and Wetlands Research Great Lakes watershed, and the popula- Ecological Concerns Fund. His work has focused primarily on the ecology of waterfowl in semi-arid envi- tion is now nearly 10,000 birds. The This rapidly growing Mute Swan popu- ronments and the staging ecology of southern Ontario population is present- lation is of concern for numerous rea- north-temperate-occurring waterfowl. ly about 2,000 birds and is increasing at sons. Mute Swans are one of the most 642 Birding • february 2002 aggressive species of waterfowl in the etation is uprooted and destroyed, fur- Management Considerations world; they regularly attack other ther decreasing the availability of food Given the similarity of climate between species of waterfowl, as well as other for native waterfowl. At high densities, Eurasia and North America, the unpar- wetland-dependent birds. They also are Mute Swans can overgraze an alleled competitive abilities of Mute known to attack humans. Mute Swans area, causing a substantial decline in the Swans, and the almost total lack of maintain large territories (>15 acres) availability of submerged aquatic vege- predators, it seems highly probable that during mating, nesting, brood rearing, tation, before they move to a new area. Mute Swans will continue to increase and foraging; they have even been In extreme cases, Mute Swans can even exponentially in the lower Great Lakes. reported to occupy territories through- eliminate some plant species from an As natural causes are unlikely to limit out the year. During incubation and ecosystem. the population in the near future, it brooding, cobs actively patrol the Mute Swans increase their feeding seems prudent to control the species in perimeter of their territory and aggres- rate during spring and summer because the Great Lakes region (and elsewhere) sively defend it, thereby forcing native more food is required before feather before the population becomes much species to nest and feed in less-preferred molt and egg laying, which probably larger. areas. influences the availability of submerged The first step that should be taken is By displacing other waterfowl from aquatic vegetation (SAV) to fall migrant to remove any legal protection for the their territories, Mute Swans reduce the waterfowl. During winter, Mute Swans species: this would allow hunters and amount of staging and breeding habitat quite likely consume nutrient storage other private individuals to participate available to native species of ducks, and overwintering structures (tubers) in control programs without a need for geese, and swans on the lower Great that could have a long-term impact on special permits. Since 1974, in Canada, Lakes. This probably reduces the carry- aquatic plant availability and species Mute Swans have been on the list of ing capacity of (with respect to number composition. For instance, perennial bird species protected under the of birds and capability of birds to species such as Vallisneria americana Migratory Birds Convention Act, 1916, acquire body fat) coastal wetlands for and Scirpus americanus overwinter as despite the fact that they are a non- staging and breeding waterfowl. Mute vegetative buds, and the survival of native species, and “Federal law does Swans have also been reported to kill these structures is the main determinant not generally protect species or families ducks, Canada Geese, Pied-billed of the next seasons growth. Therefore, that were introduced to North America Grebes, and herons, and cause nest feral Mute Swan populations reduce the by humans, i.e., not native to this conti- abandonment in Least Terns, Black carrying capacity of lower Great Lakes nent “ (Environment Canada 1991). Skimmers, Forster’s Terns, and wetlands for native waterfowl directly The species was originally listed in Common Terns. Therefore, as the quali- via aggressive interactions (reduced Canada as a means of prohibiting ty and quantity of wetland habitat con- space) as well as indirectly through releases of captive individuals. Its effec- tinues to decline in North America, resource depletion (reduced food). tiveness for this aspect is not known, increasing populations of aggressive but it has simultaneously had the effect Mute Swans serve to further reduce the of protecting the species from hunting carrying capacity of remaining habitats or harassment, thus allowing the popu- for wintering, staging and breeding lation to grow unchecked. 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 limit- ing. Whereas coastal Great Lakes wet- lands are most important as staging habitat for native waterfowl, these habi- tats are now being used year round by Mute Swans. Being primarily herbivo- rous aquatic foragers, Mute Swans con- sume 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 them- selves and their cygnets, additional veg- MUTED SWANS 643 List of Resources Control programs have been imple- ment policies similar to those of the Here are a dozen key resources for mented in a number of eastern U.S. U.S. Fish and Wildlife Service, which those birders who wish to pursue the states with varying degrees of effective- advised its managers to take effective subject. ness. Rhode Island began a control pro- steps to protect lands under their juris- gram of egg addling and pricking in diction from degradation and destruc- Allin, C. G. 1981. Mute Swans in the 1979; despite the fact that 9,378 eggs tion by Mute Swans. Atlantic Flyway. Proc. International were destroyed in 1,629 nests over a Johnson said he would like to see Waterfowl Symposium. 4:149–154. period of 22 years, the population these states adopt a program similar to Allin, C. G., G. G. Chasko, and T. P. increased by over 500 percent. that of Minnesota, which considers the Husband. 1987. Mute Swans in the Vermont, in contrast, reported no Mute species exotic, does not protect the Atlantic flyway: A review of the history, Swans in 2000, apparently as a result of birds, requires a permit for ownership, population growth, and management a lethal control program. This is sup- and sets strict standards for control of needs. Trans. Northeast. Sect. Wildl. ported by the fact that population mod- captive birds. The state presently has Society 44:32-47. els indicate that the most effective way about 15 wild Mute Swans. Wisconsin Bellrose, F. C. 1980. Ducks, Geese and to reduce population growth for a long- also does not protect the birds and Swans of North America. Stackpole lived species such as the Mute Swan is requires a permit for ownership.