Melissa Leong, National Post
December 29, 2007
The carcasses of hundreds of dead loons have washed up on the shores of the Great Lakes in recent months, and necropsies on the birds do not explicitly say what is killing one of the country's national symbols.
But the fat, healthy-looking birds have congested organs and half-digested fish in their stomachs, leading biologists to believe the loons succumbed to a spreading epidemic that has killed 75,000 birds, including 9,000 loons, in the Great Lakes since 1999.
Diseased bird carcasses appeared this year for the first time on the beaches of Georgian Bay, a wildlife expert said. Last year, the deaths were seen for the first time in Lake Michigan.
"Rather than sporadic outbreaks, which have occurred for years and years, now it is becoming much more generalized over the Great Lakes... It's becoming more widespread," said Kate Welch, a diagnostician with the Canadian Cooperative Wildlife Health Centre, who performs necropsies on the birds.
The loons, symbols of Canadian wilderness, died after eating bad fish. More specifically, the loons were poisoned with Type E botulism, a common bacteria which grows on the bottom of lakes and is spread by two non-native species. The bacteria is picked up by zebra mussels and quagga mussels which are then consumed by fish called round gobies. Loons and other fish-eating bird species become infected with the deadly bacteria when they eat the gobies.
"The thought of botulism turning the Great Lakes into killing fields, it's not a good situation," Joe Kaplan, a biologist in Hancock, Mich. told the Muskegon Chronicle.
The toxin produced by the botulism paralyzes the loons, Dr. Welch said; when they are no longer able to hold their heads up, they drown.
"The loons, which are very emblematic for Canadians, are very long-lived birds," Dr. Welch said. "They live up to 20 years or more and if we're losing a substantial number of those birds in their prime reproductive years, it may be 10 to 15 years before we see what that is going to do to the population as a whole."
Exact figures for the loon deaths are difficult to tally because the birds live almost entirely on water and many of their bodies never wash ashore to be counted, she said.
"There are probably huge numbers of mortalities that we just never see."
There are about 545,000 loons that nest each summer in Canada and while scientists do not believe they are in any immediate danger of being wiped out by Type E botulism, the outbreaks could quickly reduce their numbers. Loons produce on average less than one chick per year.
No cases of human illness have been associated with the avian botulism outbreaks that have occurred on the Great Lakes. Humans only come in contact with Type E botulism by eating infected fish or birds.
Over the years, people have been shaken by shores littered with dead loons, geese, ducks, gulls and cormorants. Horrified passersby at harbours or waterfront parks watched birds flailing around helplessly or struggling to keep their heads above water. Local media reported on the mysterious mass avian deaths.