DULUTH, Minn. (AP) — Nearly 900 loons and probably more died while migrating south across Lake Michigan last fall, and scientists suspect invasive species may be to blame.
With the iconic birds of the North Country beginning their migration back from the Atlantic and Gulf coasts in less than a month, Minnesota Public Radio reported Monday (http://bit.ly/10CYiYb ) that scientists with the U.S. Geological Survey think a complex interplay of invasive species may be the cause of the mass die-offs.
The researchers suspect invasive zebra and quagga mussels create ideal conditions in Lake Michigan for the bacteria that produces botulism toxin. The mussels filter the water so it’s incredibly clear, allowing an algae called cladophora to grow in huge amounts. Storms churn up the algae, which settle to the lake bottom and rot. That creates an environment without any oxygen, an ideal home for bacteria that produce botulism. The toxin is ingested by tiny worms and freshwater shrimp, which are eaten by fish, including the invasive round goby, which are then eaten by diving birds — including loons.
“What happens is they can’t move their muscles, and, eventually, they usually die because they can’t breathe or they can’t hold their head up out of the water,” said Stephen Riley, a fisheries biologist with the U.S. Geological Survey in Ann Arbor, Mich.
Scientists to figure out a way to break a link in that chain before it can kill more loons.
Lynette Grimes saw the problem last October as she was hiking toward Lake Michigan at Sleeping Bear Dunes National Lakeshore, outside Traverse City, Mich., where nearly 600 loons washed ashore. She and her husband worked until sunset burying them in 3-foot-deep trenches.
“The beach was just pockmarked with birds everywhere you looked,” Grimes said. “This one little peninsula had over 100 dead birds.”