WATERFORD TOWNSHIP, Mich. – State officials have eliminated poisoning as the cause of death of some mute swans at a small suburban Detroit lake and put the blame on a disease caused by a parasite.
Conservation officers have recovered eight of the birds since January from Maceday Lake in Waterford Township, northwest of Detroit, the Michigan Department of Natural Resources said.
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Necropsies on the remains of three of the swans determined that a disease caused by a parasitic flatworm killed them. The flatworm is passed to birds when they ingest certain freshwater snails, the agency said.
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It’s not certain what caused the deaths of a dozen swans this past winter at the same location, said DNR wildlife pathologist Thomas Cooley.
“But with a previous history of this disease on the lake, and open water that was available to swans to feed on snails, it is highly likely that those birds died as a result of an intestinal fluke infection,” he said.
Cooley said mortality attributed to the disease has been increasing in waterfowl nationwide, and particularly in mute swans in Michigan, either due to an increased awareness of the disease or because of an actual spreading of the parasite.
Mute swans are identified most notably by their bright, orange-colored bills and are aggressive toward humans and other wildlife. They also destroy wetland habitat and are an invasive waterfowl species in Michigan.
“Invasive species or not, we take the death of these waterfowl very seriously,” DNR law enforcement supervisor Lt. Todd Szyska said in a release. “It’s not every day we come across groups of dead waterfowl, especially in residential areas.”