Disease, Not Poison, Killed Swans In Oakland County: DNR

OAKLAND COUNTY, MI — The Michigan Department of Natural Resources has eliminated poison as the cause of death of several swans found dead in Oakland County earlier this year, officials said Wednesday.

Wildlife biologists with the DNR confirmed that a disease caused by a parasitic flatworm killed three mute swans found dead earlier this year, near Maceday Lake. Since January, eight dead mute swans have been pulled from the lake, causing some residents to believe they were ingesting antifreeze or another form of poison.

“Invasive species or not, we take the death of these waterfowl very seriously,” said Lt. Todd Szyska, DNR law enforcement supervisor in Detroit. “It’s not every day we come across groups of dead waterfowl, especially in residential areas.”

In April, People for the Ethical Treatment of Animals said it was offering a $5,000 reward for information leading to an arrest and conviction of someone in connection with the dead swans, noting that it appeared they had been poisoned. The group said nearly 20 swans had died.

Related: Nearly 20 Swans Found Poisoned, Killed In Oakland County: PETA

"These swans deserved to live peacefully with their families, but instead, they likely died in agony," PETA Senior Director Stephanie Bell said at the time. "PETA urges anyone with information about this case to come forward immediately, before anyone else gets hurt."

According to a news release issued by PETA, the dead swans have all been found floating in the lake or lying on the shoreline. A necropsy performed on one of them found that it had been poisoned, possibly with antifreeze, and police believe that the killings may be connected, PETA officials said.

But DNR officials on Wednesday said necropsies on three swans — the only ones salvageable — indicated a disease called verminous hemorrhagic ulcerative enteritis was the cause of death. The disease is caused by a parasitic flatworm that is passed to birds when they ingest certain freshwater snails, officials said.

“We can’t say for certain what caused the deaths of the dozen swans that died this past winter at the same location,” said Thomas Cooley, DNR wildlife pathologist. “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.”

The disease has been increasing in waterfowl across the nation, and particularly in mute swans in Michigan, officials said.