The other day I came across a lone Mute Swan (Anseriformes: Anatidae: Cygnus olor) in a small lake in southeast Michigan. Unlike Trumpeter Swans, Tundra Swans, and other large white waterfowl that are native to North America, these birds are actually an invasive species. They were introduced from Europe in the nineteenth century to be little more than pets in parks, zoos, and on wealthy estates. Since then they have escaped into the wild and established small but growing breeding populations around the Great Lakes, mid-Atlantic region, and in parts of the northwest.
Like many introduced species Mute Swans can upset the ecological balance of the places they invade. These large birds are aggressive and quick to chase away other animals, displacing native species. In some cases they have scared off breeding colonies and trampled the nests of endangered native birds. They also have voracious appetites and consume large amounts of aquatic plants and small animals. In some places they devour plants faster than they can grow back, degrading habitat and food sources for other animals. Some states have enacted controls to limit Mute Swan populations, including destroying eggs and culling adults. While effective at reducing their numbers and their harmful impacts, these measures have met some public opposition from those who do not understand the harm these otherwise beautiful birds can do.