Migrating waterfowl dying on Lake Onalaska
I thought this was something worth bringing to light.
By BETSY BLOOM / La Crosse Tribune
ONALASKA, Wis. — Hundreds of waterfowl again are turning up dead on Lake Onalaska, the victims of an internal parasite thought to come from eating river snails.
Since March 22, about 850 dead coots and ducks, mostly lesser scaup, have been counted on the lake, which also is Pool 7 of the Mississippi River, said Jim Nissen, La Crosse district manager for the Upper Mississippi River National Wildlife and Fish Refuge.
Some of the dead birds were sent to the U.S. Geological Survey’s National Wildlife Health Center in Madison. As before, they were found to have hundreds of trematodes, a very small fluke worm, in their digestive tract.
The trematodes use snails as an intermediate host, then are ingested by the birds when they eat the snails. One type feeds off blood and in high numbers can cause anemia or internal bleeding. Another can affect the bird’s water and electrolyte balance, leaving it vulnerable to other infections.
The birds apparently can ingest a lethal dose of worms within 24 hours, dying three to eight days after feeding on the snails. Most have been lesser scaup and coots, but Friday a refuge worker saw a dead ring-necked duck and ruddy duck, Nissen said.
Similar die-offs were seen on Lake Onalaska during migration in fall 2002 and spring and fall 2003, when more than 3,000 carcasses were found. Wildlife officials estimate more than twice that number probably died but their bodies were eaten or buried by river sand and debris.
Though only a small fraction of the population, the number of trematode deaths is discouraging, especially since most of the birds otherwise appeared to be healthy, Nissen said. “This time of year, as the birds are working to get to their nests, you hate to be picking up these dead females,” he said.
If last year was an indication, the spring toll should not be as high, Nissen said. But unlike last spring, more coots have been dying this year. The numbers do appear to be tapering off, he said, as the flocks continue to move north.
Eagles, gulls and crows have been seen eating the dead birds, but are not thought to be at risk of picking up the parasites.
Any sick or dead birds found on the river should be reported to the La Crosse District office of the U.S. Fish and Wildlife Service at (608) 783-8405.
