The loon, an icon of the north and Minnesota's state bird, is dying by the thousands across a growing swath of the Great Lakes, victims of a bacterial disease that works its way up from the lake floor.
First noticed in the eastern portion of the Great Lakes chain eight years ago, death is now spreading west. So far, loons have not suffered die-offs in Lake Superior, but officials are concerned about the potential in Duluth-Superior harbor.
"You begin to wonder year after year how much that population can withstand if you're losing large numbers of adult birds," said Helen Domske, extension specialist for the New York Sea Grant.
This year the area of dead birds has spread to hundreds of miles of pristine Lake Michigan shoreline. Last month, so many dead loons and other birds washed up on the shores of a Pennsylvania state park that officials used a local funeral home to incinerate them.
"Loons are such a beautiful bird, and to see a hundred of them laying on the beach, it just really disturbs people," said Harry Leslie, operations manager at Presque Island State Park near Erie, Pa.
As popular as loons are, Domske said, no one knows how large their populations are in northern Canada or how many have died during the past several years.
Thousands may expire on the lakes and sink, she said, and others wash up in remote areas or along Canadian shores and are never counted. From those that are collected and bagged, said Domske, it's clear that Michigan, Ontario, New York and Pennsylvania have all had substantial die-offs this year.
Scientists believe that the birds are killed by Type E botulism that works its way up the food chain from the bottom of the lake. There, naturally occurring botulism spores germinate and grow into toxin-producing bacterial cells. Those bacteria move into quagga mussels as they filter the water.
Then a small fish called a round goby picks up the bacteria by eating the mussels.
When loons, long-tailed ducks, gulls, grebes and other birds eat the infected fish, the toxin enters their systems, paralyzing the birds. Within hours they can no longer fly or hold their necks up, and they drown.
A murderous migration
The adult loons spend the summer in northern border states and Canada and migrate across the Great Lakes in October and November.
Mark Breederland, Michigan Sea Grant extension educator, said that 200 loons were among 2,900 dead birds picked up last year along 11 miles of Sleeping Bear Dunes National Lakeshore. This year, more than twice that number have been found in the area and farther north, with reports of additional deaths spread across much of Lake Michigan's northern shoreline. "This really has people worked up."
Joe Kaplan, a biologist and co-director of the nonprofit Common Coast Research and Conservation, said that volunteers canvassed 95 miles of northern Lake Michigan beach between late October and Nov. 18 and counted 2,092 dead birds, including 517 loons.
The organization monitors banded loons in the Upper Peninsula, Kaplan said, and 97 percent of them typically return to their breeding territories each spring. "We'll be keeping an eye on the rate at which adult birds return next year," he said.
Kaplan is also concerned about foxes, coyotes, eagles and other wildlife that scavenge the decomposing birds and in some cases have been found dead near them.
Looking at various suspects
Because neither quagga mussels nor round gobies are native to the Great Lakes, the problem has been described as another unseen threat from invasive species.
Researchers are also studying whether higher lake temperatures and lower water levels in recent years may be stimulating more plant growth, thereby increasing the amount of bacteria on lake bottoms as the plants die, sink and decompose.
Amy McMillan, who teaches biology and researches population genetics of loons at Buffalo State College, said she and others have watched the bird die-offs spread through four of the five Great Lakes. "All of these lakes are such major flyways for migratory birds, among the largest in the world," she said. "That's very frightening."
The area near Duluth is also a major flyway, but so far there have been no reports of die-offs in loons or other birds, said Doug Jensen, aquatic invasive species coordinator for the Minnesota Sea Grant program. "It's very much a concern, and we're keeping a watchful eye," he said.
The Duluth-Superior harbor contains zebra and quagga mussels as well as round gobies, he said.
"There is no reason to believe that Duluth-Superior harbor would be immune to Type E botulism," Jensen said.
Tom Meersman • 612-673-7388