By MICHELLE MERLIN email@example.com
Traverse City Record-Eagle
---- — TRAVERSE CITY -- The common loon, horned grebe and scores of other waterfowl briefly take respite in Michigan waters as they migrate south.
Their stops too often ended here in recent years as many fell victim to a paralytic disease and washed up dead along Lake Michigan beaches. This year it appears they’ve largely evaded that serious health threat.
Experts said avian botulism claimed far fewer waterfowl this year than last year -- so far, about 420 dead birds have been found on the shores of Sleeping Bear Dunes, compared to about 1,000 at the same time last year.
Overall, at least 3,947 birds were found dead along the Michigan shoreline in 2012, 1,500 of those in Sleeping Bear Dunes. The lower death toll in 2013 pleased those who study avian botulism.
“This year was just beautiful,” Dan Ray, the avian botulism monitoring project lead at the Sleeping Bear Dunes National Lakeshore, said.
Botulism enters the marine food chain in the Great Lakes, and birds that eat fish and bottom-feeders, especially the invasive gobi fish, are susceptible. The bacteria cause a bird’s nervous system to deteriorate, making infected birds unable to fold wings or hold up their heads. Eventually the bacteria make it hard for birds to breath and their hearts fail.
This year about 30 dead loons were discovered at Sleeping Bear Dunes, compared to 500 last year.
Lower infection levels are a real boon for the loons, which have a longer maturation cycle and lower reproduction rate than most other birds.
“It’s really healthy for the bird species' reproduction that adults that are capable of reproduction aren’t getting taken out of the population so they can go out and have a good reproduction cycle,” said Mark Breederland, a Michigan Sea Grant educator.
Tom Cooley is a wildlife biologist and pathologist at the Department of Natural Resource’s Wildlife Disease Lab in Lansing. He tests dead birds for botulism, and mainly sees infected adult loons.
The botulism season isn't quite over; it runs from June through the end of November, adn the past two weeks or so have been among the worst for birds. Ray counted 272 dead birds by the end of October, and in the last few weeks that number has climbed by another 100-plus.
“At this point, hopefully, the birds staged on a portion of Lake Michigan have left,” said Cooley.
Researchers continue to try to determine what causes variations in infection numbers from year-to-year. For example, 2,677 birds died of avian botulism in 2010, while fewer than 200 died in 2009 and 2008.
Breederland said infections can be linked to four influences: low lake levels, high water temperatures, nuisance algae, and invasive species.
“We think these things are all interwoven,” Breederland said.