A recent die-off of hundreds of waterfowl in eastern Lake Ontario is caused by Type E avian botulism, the New York State Department of Environmental Conservation has found. Particularly affected are gulls and Caspian terns.

There have been no documented botulism deaths on the Canadian side of the lake during this die-off, says Dr. Katherine Welch of the Canadian Cooperative Wildlife Health Centre at the University of Guelph. The situation is being monitored.

Health risks to humans are minimal, Welch said, because the toxin has to be ingested. Anyone handling dead birds should use gloves or an inverted shopping bag, and wash thoroughly afterwards.

Welch told CBC.ca that these waterfowl deaths occur sporadically in the Great Lakes. In October, more than 500 loons were killed by botulism after eating infected fish. The disease paralyzes the birds, causing them to drown.

"The die-offs are becoming more common. We first saw them in the late 1990s. They're increasing in frequency and expanse over the last few years," she said. They affect any fish-eating birds or scavenger birds, including double-crested cormorants, ducks, loons, grebes and birds from the gull family.

The deaths are a concern because they can affect the sustainability of the bird populations.

"It's a risk, especially with birds like the Caspian tern that aren't large populations. If the adult dies, the nestlings die because there's no one to feed them," Welch said. "If a large enough population of adult birds die off, it could have a significant impact on the population."

Invasive species

These large-scale bird deaths are due to invasive species such as zebra mussels and round gobies. The zebra mussels create a low-oxygen environment where the toxin can grow, then round gobies, a bottom-dwelling fish, eat the zebra mussels and the disease works its way up the food chain to birds.

Fish with the disease swim differently and make themselves more obvious targets to the birds, meaning that birds are more likely to eat infected fish and thus contract botulism.

There's little that can be done to stop the deaths. "Until there's some change in the ecosystem of the Great Lakes, it's going to be a problem," Welch said.

She says that anyone who finds more than two dead or sick birds should notify Canadian Wildlife Services or the Cooperative Wildlife Health Centre.