Description
Potentially Misidentified Species - In the Chesapeake Bay region, the only similar species is the native Tundra (or Whistling) Swan, Olor columbianus (Birkhead and Perrins 1986; Stewart and Robbins 1958).
Taxonomy
| Kingdom | Phylum | Class | Order | Family | Genus |
|---|---|---|---|---|---|
| Animalia | Chordata | Aves | Anseriformes | Anatidae | Cygnus |
Synonyms
Invasion History
Chesapeake Bay Status
| First Record | Population | Range | Introduction | Residency | Source Region | Native Region | Vectors |
|---|---|---|---|---|---|---|---|
| 1962 | Established | Expanding | Introduced | Regular Resident | Europe | Eurasia | Ornamental(Pet Release) |
History of Spread
The native range of Cygnus olor (Mute Swan) includes southern Scandinavia, Great Britain, and France west to Poland, and scattered populations in Russia and China. This swan has been introduced in North America, South Africa, Australia, and New Zealand (Johnsgard 1978). These birds are widely kept in zoos and as ornamental birds in parks and estates.
Breeding pairs of feral Cygnus olor were first reported from North America in NJ in 1916; in NY (probably Long Island) in 1919, Martha's Vineyard, MA in 1922, Block Island, RI in 1923, and by the 1950's in CT, VA, and DE. This swan were first noted in the Atlantic Flyway winter waterfowl census in 1950, and their counts grew at an annual rate of 5% from 1954 to 1963 (Allin et al. 1987; Teale 2011). In subsequent decades, 1964-73 and 1974-83, the growth rate was 9.4 and 7.1% respectively. By 1986, feral C. olor were found from ME to GA, with the greatest numbers in MA, RI, CT, NY, and NJ (Allin et al. 1987). In New England states, because of concerns about effects on native waterfowl, state fish and game agencies have started control programs, mostly involving shaking of eggs to prevent hatching (Allin et al. 1987). Separate C. olor introductions occurred in Traverse City, MI (Stewart and Robbins 1958); MN, WI, WY, Ontario, and British Columbia (Conover and Kania 1994). The main centers of population in North America are the north- to mid-Atlantic U.S. coast, and the Great Lakes (Peterson 1980, Sauer et al. 1996).
Three C. olor were sighted near Ocean City, MD in 1954, and three more immature birds near Gibson Island, MD (Anne Arundel County) in 1955 (Stewart and Robbins 1958). In 1962, during a storm, five pinioned swans escaped from estates along the Miles River, Talbot County MD, and bred successfully, starting a population which reached ~ 400 birds by 1980. If estimated rates of growth have been maintained, this population would be ~ 2000 birds in 1996 (Reese 1980). Numbers of adults, counted in summer 1986, were 200 birds in MD and 60 birds in VA. A target population of ~ 400 birds was set by the Maryland Department of Natural Resources (Allin et al. 1987), but public protest has hindered control programs. By 2000, the MD population exceeded 4,000 birds, with control methods still under study (Hindman 2000).
A federal court decision, in 2001, complicated management of C. olor populations by holding that this bird is covered under the Migratory Bird Treaty Act, and so should be regulated by the United States Fish and Wildlife Service (USFWS). Consequently, state management plans now require federal approval. MD's management plan involves lethal means (euthanasia) and nonlethal methods (sterilization, egg addling, etc.), to remove swans from designated "swan-free areas" and to reduce the reproduction of remaining populations. This plan was approved by USFWS on Aug. 11 2003, but was then delayed by a federal court injunction on Sept. 9th 2003 (Maryland Department of Natural Resources 2003). In December, 2004, in Congress, an amendment was passed, to an omnibus federal spending bill, which removed an ambiguity under the Migratory Bird Act, permitting swan control plans to go forward (Thomson 2004). Control programs have continued to the present, and the number of breeding swans in Maryland has been reduced to few hundred by 2009. The Maryland Department of Natural Resources plans to continue eradication (Halsey 2009; Wood 2009).
History References - Allin et al. 1987; Conover and Kania 1994; Halsey 2009; Hindman 2001; Johnsgard 1978; Maryland Department of Natural Resources 2003; Peterson 1980; Reese 1979; Reese 1980; Sauer et al. 1996; Stewart and Robbins 1958; Thomson 2004
Invasion Comments
Ecology
Environmental Tolerances
| For Survival | For Reproduction | |||
|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | |
| Temperature (ºC) | ||||
| Salinity (‰) | 0.0 | 35.0 | 0.0 | |
| Oxygen | ||||
| pH | ||||
| Salinity Range | fresh-eu |
Age and Growth
| Male | Female | |
|---|---|---|
| Minimum Adult Size (mm) | 1250.0 | 1250.0 |
| Typical Adult Size (mm) | 1375.0 | 1375.0 |
| Maximum Adult Size (mm) | 1500.0 | 1500.0 |
| Maximum Longevity (yrs) | 50.0 | 50.0 |
| Typical Longevity (yrs | 9.0 | 11.0 |
Reproduction
| Start | Peak | End | |
|---|---|---|---|
| Reproductive Season | |||
| Typical Number of Young Per Reproductive Event |
|||
| Sexuality Mode(s) | |||
| Mode(s) of Asexual Reproduction |
|||
| Fertilization Type(s) | |||
| More than One Reproduction Event per Year |
|||
| Reproductive Startegy | |||
| Egg/Seed Form |
Impacts
Economic Impacts in Chesapeake Bay
Cygnus olor (the Mute Swan) has had increasing impacts in the Chesapeake Bay area at present, and these are likely to become more widespread as populations increase. Specific impacts in the Chesapeake area have not been been studied, so that much of the information below comes largely from New England and Europe. Most of these impacts are likely to occur in the Chesapeake region.
Fisheries, Habitat Change- Cygnus olor is an unprotected species in VA and DE and presumably can be hunted legally there, but not in MD (Allin et al. 1987). These swans affect fish and wildlife resources through their consumption of submerged aquatic vegetation, and through exclusion of other waterfowl from large areas around their nesting sites. They do not eat fish, and rarely consume fish eggs. They may be beneficial in very weedy areas by consuming excess vegetation and opening space for fish to move. The vegetation eaten by C. olor is quickly recycled in the form of nutrient-rich droppings (Birkhead and Perrins 1986).
On the other hand, very dense populations, particularly those receiving much human food, could stimulate phytoplankton growth, leading to a degradation of water quality. Cygnus olor exclude other waterfowl from breeding areas, and may be territorial year-round, affecting the feeding of both breeding and wintering ducks (Conover and Kania 1994), and hence could have an adverse impact on duck-hunting (Allin 1987).
Industry (Agriculture)- Cygnus olor may occasionally graze in fields, sometimes damaging crops (Birkhead and Perrins 1986).
Aesthetic- Cygnus olor is a paragon of beauty in Western art and culture. Its grace and its relatively harmonious family life appeal to adults and children alike. Residents in areas with introduced C. olor populations are often very protective of 'their' birds. In a survey of 300 randomly selected people in three New England cities, 50% wanted more Cygnus olor in their neighborhood and only 5% wanted fewer, only 45% knew it was an exotic species, and 66% thought that its exotic status should not affect its management (Conover and McIvor 1993). Consequently, resistance to control measures is high. In the Chesapeake Bay region, efforts to control swan populations on the MD Eastern Shore have been strongly resisted by by residents (Williams 1997).
Health - Dense populations of C. olor may result in high coliform counts, affecting the quality of water for swimming and shellfishing. Aggressive territorial Cygnus olor may attack people, rarely causing injury to adults, but posing more danger to children (Allin 1987; Birkhead and Perrins 1986; Willey and Halla 1973).
In states which are actively managing Cygnus olor populations, control methods include shaking of eggs, euthanasia of injured birds, and sometimes pinioning (removing flight feathers), sterilization, or killing of 'problem' birds (Allin 1987). Proposals for hunting or deliberate killing of adult birds tends to be highly unpopular.
References - Allin 1987; Birkhead and Perrins 1986; Conover and Kania 1994; Conover and McIvor 1993; Willey and Halla 1973; Williams 1997
Economic Impacts Outside of Chesapeake Bay
At present Cygnus olor (Mute Swan) populations and economic impacts in North America are greatest in New England and NY (Allin 1987; Williams 1997). Impacts in these areas are qualitatively the same as those discussed for Chesapeake Bay. While negative impacts of C. olor are widely recognized by state management agencies, wildlife biologists, birders, and many environmentalists, protests by resident animal lovers have greatly hindered effective management of this beautiful bird in North America (Allin 1987; Williams 1997). In Australia, C. olor is believed to be competing with the native C. atratus (Black Swan) (Lever 1987).
References- Allin 1987; Lever 1987; Williams 1997).
Ecological Impacts on Chesapeake Native Species
Cygnus olor (the Mute Swan) has developed locally dense populations in the northeastern United States as well as its native Eurasian habitat. Their impact is large, in part because of the bird's size (the world's largest flying bird), their limited movements, and their territorality during breeding (Birkhead and Perrins 1986; Willey and Halla 1972). Most data on their ecological impacts comes from Europe and New England.
Herbivory- Cygnus olor feed largely on submersed vegetation, but also eat marsh and, rarely, terrestrial plants. In coastal areas in England, soft, succulent salt marsh plants (Trigochin sp.- Arrowgrass; Puccinellia sp.- Alkaligrass; Plantago maritima- Seaside Plantain) were eaten selectively in early spring and summer; and the seagrasses Zostera marina (Eelgrass), Ruppia maritima (Widgeongrass), and the seaweed Enteromorpha sp. were preferred in summer (Birkhead and Perrins 1986). Cygnus. olor in RI estuaries fed on Z. marina, Ruppia maritima, Enteromorpha sp., Ulva sp., and other algae (Willey and Halla 1972). In freshwater areas and the Baltic, foods include typical freshwater SAV species, such as Potamogeton spp., Myriophyllum spicatum (Eurasiian Watermilfoil) Ceratophyllum demersum (Coontail), Elodea sp. (Waterweed), Vallisneria sp. (Wild Celery), and Chara sp. (Stonewort) (Birkhead and Perrins 1986; Willey and Halla 1972) and marsh species such as softer grasses (Alopecurus sp., Agrostis sp.) and plants with starchy roots (e.g. Rorippa spp.) (Birkhead and Perrins 1986).
Cygnus olor kept in pens on RI coastal ponds consumed an estimated 3.8 kg (wet weight) of vegetation per swan per day, but still lost weight (Willey and Halla 1972). However, efforts to measure the effect of swan consumption on plant biomass, usually by means of exclosures, are often inconclusive either because swan populations were too small to affect vegetation biomass, or because nutrients excreted by swans are rapidly recycled by growing vegetation (Birkhead and Perrins 1986; Conover and Kania 1994). As C. olor populations increase on the Atlantic seaboard, adverse effects on submersed vegetation may become more apparent (Allin et al.1987; Cobb and Harlin 1980). At present, MD's C. olor population is estimated to consume 5 million kg of submerged aquatic vegetation per year (Hindman 2001).
Competition - Cygnus olor feed on many of the same plants as other wintering herbivorous waterfowl, but competition at this time of year is minimized by the fact that their long necks enable them to feed at greater depths than dabbling ducks or geese, but still at shallower depths than those used by diving ducks such as the Canvasback (Athya vallisneria). However, ice can force these birds to aggregate in small areas of open water, and changing depth with tides may result in the same patch of vegetated bottom being grazed by swans and ducks, intensifying competition (O'Brien and Askins 1985). In Chesapeake Bay, C. olor are believed to be competing with the smaller and less aggressive Olor columbianus (Tundra Swan) (Williams 1997). However, it is unclear whether competition or other factors are responsible for the 30% decline of O. colombianus since the mid-1970s (Hindman 2001).
During the breeding season, competition with other waterfowl is much more apparent because of C. olor's aggressive territorality. Cygnus olor can exclude other waterfowl from nesting or feeding in areas of 0.2 to 4.8 ha (average territory size = 1.8 ha). Territorial defense may range from agressive postures to killing of offending birds (Birkhead and Perrins 1986; Willey and Halla 1972). Native breeders likely to be affected include Anas rubripes (American Black Ducks), A. strepera (Gadwalls), and A. discors (Blue-winged Teal) (Stewart and Robbins 1958; Wass 1972). However, exclusion of breeding birds of other species appears to be variable and is not always observed (Conover and Kania 1994). In the Chesapeake Bay aggressive behavior by C. olor is believed to have eliminated breeding colonies of state-threatened Sterna antillarum (Least Terns) and Rhynchops niger (Black Skimmers) (Williams 1997).
Habitat Change - Cygnus olor have potential effects on aquatic habitats through eating and tearing up submersed and marsh vegetation, by trampling marsh vegetation, and through excretion of large quanties of nutrients into the water. Effects on submersed vegetation appear to be a function of population size. At least at low swan densities, rapid recycling of nutrients may result in accelerated plant growth, compensating for grazing (Birkhead and Perrins 1986). Higher densities of swans, or urban and suburban populations fed human food, may be more likely to alter plant communities directly through grazing, or indirectly, through promoting growth of phytoplankton and epiphytes. Territorial exclusion during breeding may actually reduce damage to vegetation by eliminating grazing by flocks of non-breeding swans and other waterfowl (Cobb and Harlin 1980).
References - Allin et al.1987; Birkhead and Perrins 1986; Cobb and Harlin 1980; Conover and Kania 1994; Hindman 2001; O'Brien and Askins 1985; Stewart and Robbins 1958; Wass 1972; Willey and Halla 1972; Williams 1997
Ecological Impacts on Other Chesapeake Non-Native Species
Competition - Introduced breeding populations of Anas platyrhynchos (Mallard Duck) and Branta canadensis (Canada Geese) may be excluded from breeding and feeding sites by nesting Cygnus olor (Mute Swans) (Birkhead and Perrins 1986; Willey and Halla 1972). Competition in winter is normally minimized because C. olor, with its longer neck, feeds in deeper water, but may occur when birds are crowded together by ice, or when the changing tide permits swans and ducks to graze the same patch of bottom (O'Brien and Askins 1985). During the breeding season, C. olor have been documented killing ducklings of Anas platyrhynchos (Mallards) and goslings of Branta canadensis (Canada Geese) (Hindman 2001).
Herbivory - The submersed plant Myriophyllum sp. (possibly the introduced M. spicatum- Eurasian Watermilfoil) was among species eaten by C. olor in RI and Sweden (Birkhead and Perrins 1986;Willey and Halla 1972). Other introduced submersed plants are probably grazed by C. olor in Chesapeake Bay. Tundra Swans and Canada Geese were among waterfowl observed feeding in areas dominated by Hydrilla verticillata (Hydrilla) (Hench et al. 1994), so C. olor are likely to graze on this species also.
References - Birkhead and Perrins 1986; Hench et al. 1994; O'Brien and Askins 1985; Willey and Halla 1972
References
Allin, Charles C.; Chasko, Gregory C.; Husband, Thomas P. (1987) Mute swans in the Atlantic Flyway: A review of the history, population growth, and management needs., Transactions of the Northeast Section, The Wildlife Society : 32-46Birkhead, Mike; Perrins, Christopher (1986) The Mute Swan, In: (Eds.) . , London. Pp.
Cobb, J. S.; Harlin, M. M. (1980) Mute swan (Cygnus olor) feeding and territorality affects diversity and density of rooted aquatic vegetation, American Zoologist 20: 882
Conover, Michael R.; McIvor, Donald E. (1993) Exotic species in urban environments: lessons from New England's mute swans, In: (Eds.) . , Washington, D.C.. Pp. 87-90
Conover, Michael; Kania, Gary S. (1994) Impact of interspecific aggression and herbivory by mute swans on native waterfowl and aquatic vegetation in New England, The Auk 111: 744-748
Hench, John E.; Gibbs, Ron; Hench, Jayne S. (1994) Some observations on Hydrilla and wintering waterfowl in Montogomery County, Maryland, The Maryland Naturalist 38: 3-9
2001 Mute swans- Beautiful but controversial birds.. Web address://www.dnr.state.md.us/wildlife/muteswans.html
Johnsgard, Paul A. (1978) Ducks, Geese, and Swans of the World, , Lincoln. Pp.
Lever, Christopher (1987) Naturalized birds of the world., , London. Pp.
O'Brie, Maria; Askins, Robert A. (1985) The effect of Mute Swans on native waterfowl, Connecticut Warbler 5: 27-30
Peterson, Roger T. (1980) A guide to the birds, , Boston. Pp.
Reese, Jan G. (1975) Productivity and management of feral Mute Swans in Chesapeake Bay., journal of Wildlife Management 39: 280-286
Reese, Jan G. (1976) Population ecology of mute swans in Chesapeake Bay., National Geographic Research Reports 17: 745-750
Reese, Jan G. (1980) Demography of European Mute Swans in Chesapeake Bay., The Auk 97: 449-464
Robbins, Chandler S.; Blom, Eirik A. T. (1996) Atlas of the Breeding Birds of Maryland and the District of Columbia, , Pittsburgh. Pp. 70-305
1996 The North American Breeding Bird Survey.
Sousa, and 6 authors. (2007) Genetic and shell morphological variability of the invasive bivalve Corbicula fluminea (Muller, 1774) in two Portuguese estuaries., Estuarine, Coastal and Shelf Science 74: 166-174
Stewart, Robert E.; Robbins, Chandler S. (1958) Birds of Maryland and the District of Columbia., , Washington D.C.. Pp.
Teale, Chelsea L. (2011) A revised account of initial mute swan (Cygnus olor) introductions to the northeastern United States, Biological Invasions 13: published online
Wass, Melvin L. (1972) A checklist of the biota of lower Chesapeake Bay, Special Scientific Report, Virginia Institute of Marine Science 65: 1-290
Willey, Charles H.; Halla, Bernard F. (1972) Mute Swans of Rhode Island., , Providence, RI. Pp.
Williams, Ted (1997) The ugly swan., Audubon 99: 26-32