In this file photo, the male swan keeps watch as the female keeps the hatching eggs and the newborn signets warm in the nest.
Cathie Coward / Spectator Staff
There have been numerous cases of lead poisoning in swans at LaSalle Park over the years. The lead is thought to be from shot used by hunters or lead sinkers used by anglers.
In this file photo, the male swan keeps watch as the female keeps the hatching eggs and the newborn signets warm in the nest.
Cathie Coward / Spectator Staff
In this file photo, the male swan keeps watch as the female keeps the hatching eggs and the newborn signets warm in the nest.
Barry Gray / Spectator Photo Assignment Fulfi
There have been numerous cases of lead poisoning in swans at LaSalle Park over the years. The lead is thought to be from shot used by hunters or lead sinkers used by anglers.
Necropsy tests on four swans and a snow goose that died mysteriously around Hamilton Harbour in January have ruled out lead as the culprit, saying a form of botulism was likely to blame.
However, a separate test on a juvenile eagle - found in distress at Christie Conservation Area in the same month, and later died - did find lead poisoning to be the cause of death. Results were unavailable from a second juvenile eagle that was found in lethargic state in Cootes Paradise in January and later died.
The C. botulinum results are particularly interesting because they may signal an outbreak of the bacteria in the harbour. There could be other avian deaths - swans and other waterfowl - that have died from C. botulinum but not come to the attention of authorities.
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The report from the Canadian Wildlife Health Co-Operative at the University of Guelph says zebra mussels likely played a role, that the creatures consumed the bacteria through feeding to be in turn eaten by the birds. A large quantity of the mussels was found in the digestive system of one of the swans.
“It can find its way in to soils, and zebra mussels can be the vector,” said Pam Martin, manager of Environment Canada’s Wildlife Toxicology Research Centre, which is looking into the deaths. She also said it is unusual to have birds die from botulism in winter. It’s usually something that happens in warmer months.
Bev Kingdon - of the Trumpeter Swan Restoration Group, a volunteer organization that keeps an eye on swans at LaSalle Park - said there have been numerous cases of lead poisoning in swans over the years. The lead is thought to be from shot used by hunters or lead sinkers used by anglers.
But botulism as a cause of death is something she had not heard before. “I don’t know anything about botulism, but to have that many swans die at one time is a concern.
Large populations of trumpeter and mute swans - sometimes more than 200 - spend winters at LaSalle Park in Burlington.
But almost all fly north in the spring, she says, to return in the fall. She says there are about a half-dozen swans at LaSalle Park these days.
The C. botulinum bacterium is thought to develop on putrefying animal carcasses, which attract maggots that find their way into the food chain to be consumed by swans or other waterfowl. When those birds die, the cycle is repeated over and over again, and this sometimes leads to huge numbers of avian deaths.
In one particularly serious outbreak, along the shores of Old Wives Lake in Saskatchewan in 1998, an estimated one million waterfowl of different species died from botulism poisoning.
In the case of the local swan and snow goose deaths, scientists had a hard time making a definitive conclusion.
“This is an extremely challenging case series to determine a definitive cause of death. In all five birds ... there were no distinct abnormalities noted,” a report said.
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“Based on all this information, the most likely cause of death in these birds is type C botulism; however, this is not a definitive diagnosis and a different toxicity is still possible,” the report said.
A spokesperson from the Canadian Wildlife Health Co-Operative could not be reached for comment.
is a retired, award-winning Spectator journalist who writes about local history and heritage as a contributing columnist. Mark is also a celebrated singer-songwriter and storyteller who performs shows that feature his songs about characters and events from Hamilton’s past that are often the focus of his “Flashbacks” column.
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