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Swans - Conservation Of Swans

birds lead species waterfowl

Although swans are not abundant birds, during migration and winter these birds may congregate in large numbers. Moreover, swans are large animals, and they are relatively easy to approach on land when they are husbanding their young, or on water when they are in molt. Because of these factors, wild swans have long been hunted for subsistence or sport. However, because of their low reproductive potential, populations of swans are easily depleted and extirpated by overhunting. This occurred during the heyday of sport and market hunting of the nineteenth century, a population decline that was exacerbated by the widespread loss of breeding, migrating, and wintering habitats. Some species of swans, including the trumpeter swan of North America, became an endangered species, and were almost made extinct. More recently, however, the populations of most species of swans have generally been stable or have increased A tundra swan (Cygnus columbianus) at the Kellogg Bird Sanctuary, Michigan. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. due to conservation efforts by government, especially during the latter half of the twentieth century. Today, there is no legal hunt of swans in North America, although there is some poaching of these birds, and a small aboriginal harvest of tundra swans occurs on their breeding grounds.

Swans are also at risk from other environmental stresses. The occurrence of lead pellets from spent shotgun ammunition in the surface sediment of their wintering habitat poses a toxic risk for wild swans. Waterfowl are poisoned when they retain the lead shot in their gizzard for use in grinding their food of seeds. This results in the abrasion and dissolving of the lead, which enters into the bloodstream and can cause a range of toxic problems, including death (see entry on ducks). During the 1980s and 1990s, it is likely that hundreds or thousands of swans have died each year in North America from poisoning by lead shot, and probably more than a million ducks and geese. Fortunately, the use of lead shot has been, or soon will be banned over most of North America, so this will be less of a problem in the future.

Swans are also vulnerable to certain types of infectious diseases, especially avian cholera. This disease is caused by a food- and water-borne pathogen, and it can occur as a local epidemic that kills tens of thousands of waterfowl on particular lakes. Potentially, the trumpeter swan is especially at risk from the effects of this sort of epidemic disease, because large numbers congregate on wintering grounds in only a few lakes in Montana, Idaho, and Wyoming. Birds wintering on coastal estuaries are at less risk from avian cholera.

Because of their positive aesthetics, swans have been widely cultivated in waterfowl collections and in public parks. The most commonly kept species is the mute swan, but other species are also bred, including the unusual black swan (Cygnus atratus) of Australia. Viewings of wild swans are also widely sought after by birders and other naturalists. Both the cultivation of swans and their non-consumptive use in ecotourism have economic benefits, and do not endanger populations of these birds.


Resources

Books

Godfrey, W.E. The Birds of Canada. Toronto: University of Toronto Press, 1986.

Johnsgard, P.A. Ducks in the Wild: Conserving Waterfowl and Their Habitats. Swan Hill Press, 1992.

Owen, M., and J. M. Black. Waterfowl Ecology. London: Blackie Pub., 1990.

Sibley, David Allen. The Sibley Guide to Birds. New York: Knopf, 2000.


Bill Freedman

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