Story originally printed in the Winona Daily News or online at www.winonadailynews.com
Published - Friday, October 26, 2007
Massive bird die-off tied to invasive snail
 Calvin Gehri, biologist technician with the US Fish and Wildlife Service, piles dead waterfowl in the front of his boat Thursday along the banks of Broken Gun Island in Lake Onalaska. The birds, American Coots, fell victim to a parasite in the faucet snails they ate. (Photo by Melissa Carlo/Winona Daily News) |
FRENCH ISLAND, Wis. — Circling high over Lake Onalaska, two eagles fought over an American coot in one of the eagles’ talons.
The eagle lost its grip, and the coot plunged into the water near Broken Gun Island. It bobbed to the surface but made little effort to escape as the eagles swooped overhead.
“He’s probably sick and they know it. It’s easy pickings around here,” said Calvin Gehri, a biological technician with the U.S. Fish and Wildlife Service’s La Crosse District.
The dying coot would soon join the thousands of dead waterfowl Gehri and other refuge staff have collected along the shores of the Mississippi between Dresbach, Minn., and northern Iowa.
More than 25,000 birds — mostly coots and scaup — have died on the upper Mississippi River since 2002 as a result of eating faucet snails that carry an intestinal parasite, according to federal wildlife officials. From 2005 to 2006, there was a 16-fold increase in bird deaths in pools 8 and 9. Last fall, there were an estimated 5,000 bird deaths in the area between La Crescent, Minn., and MacGregor, Iowa.
Faucet snails are found along the Mississippi between Nelson, Wis., and Fulton, Ill., but the highest concentration of the infected snails is in the La Crosse region. More recently, they’ve been found downriver as well.
Wildlife experts are trying to figure out how to get rid of the snails without affecting native snails. Last year, the FWS tried covering underwater rocks with sand and gravel in an attempt to reduce the snails’ habitat.
There aren’t enough snails between Wabasha, Minn., and Winona to create a large die-off of birds, said Mary Stefanski, Winona district manager for the FWS. She said the problem snails tend to follow the water downstream.
The exotic snails came to the Great Lakes region from Eastern Europe in the late 1800s. The species got its name when it invaded municipal water systems, Gehri said. It’s unknown how the snails got into the Mississippi, though most aquatic invaders are carried in ships’ ballast water.
Wildlife staff first noticed a water bird die-off in Lake Onalaska in 2002, said Jim Nissen, La Crosse FWS district manager. Since then, there has been a multi-agency effort to track down the faucet snail trail.
Scientists from the U.S. Geological Survey’s National Wildlife Health Center and Upper Midwest Environmental Sciences Center are working with local agencies to monitor the faucet snail population. Professors and students from the University of Wisconsin-La Crosse and Minnesota State College-Mankato have conducted sideline studies on distribution.
They’ve discovered that two varieties of trematodes, a kind of fluke worm, infect the snails, which can host up to 100 of the parasites; birds can get a lethal dose in less than 24 hours of feeding and die within three to eight days.
Infected birds die from blood loss, shock from a chemical imbalance or a stomach infection. Nissan said there’s no way to save an infected bird.
“It’s pretty sad when you see a sick one. They can’t swim. They can’t dive,” Gehri said. “Some are like a decoy and you can pick (them) up with your bare hands. Some will maybe flock a bit, but they’re so sick it’s all they can do.”
As with most exotic species, eradication is difficult without disturbing natives species. But Gehri said the declining bird population is cause for concern.
Last week, Gheri collected about 200 dead coots along the bank of Broken Gun Island. On Thursday, he picked up 160, a fraction of the birds floating among wild celery and algae.
Carcasses dropped by eagles hung in trees on the island, and feathers littered the shore.
Predatory birds are apparently immune to the parasite, scientists say. About 25 eagles loomed above, waiting for a second go at the coots Gheri didn’t pick up.
The dying coot that dropped from an eagle’s talons slowly disappeared around the island’s corner. When Gehri circled the island, it was gone.
Contact reporter Amber Dulek at amber.dulek@lee.net or (507) 453-3513.
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