Scaup still dying at Winnie…
Grand Rapids, Minn. — When an intestinal parasite in the fall of 2007 killed thousands of scaup at Lake Winnibigoshish, it marked the first time trematodes were blamed for a large-scale die-off in north-central Minnesota.
Additional scaup and coots have died every spring and fall since.
“When we get a good batch of birds sitting on the west side (of Winnie), bad things can happen very fast,” said Perry Loegering, DNR area wildlife manager in Grand Rapids.
But it’s not limited just to Lake Winnibigoshish. DNR officials also have recovered dead birds on Bowstring Lake, and have received reports of dead scaup on Round Lake, too.
Those lakes, all relatively shallow, with sandy bottoms, form “the trifecta of scaup lakes in northern Itasca County,” Loegering said.
Faucet snails, an invasive snail that serves as a host for the parasites responsible for killing scaup, have been found in Winnibigoshish and Bowstring. The intestinal parasites that kill the birds are known as trematodes. They have a complex life history and require two hosts to develop.
When scaup eat a snail that’s infected, the parasites attach to the bird’s intestinal walls and feed on their blood, killing the bird.
“As far as what to expect this fall, that’s kind of an unknown,” said Steve Cordts, DNR waterfowl specialist.
“The scaup migration here in Itasca County seemed to be fairly stable, or predictable,” Loegering said. “We always had a fairly nice group that would stay on Bowstring for an extended period of time.
And then we’d have these erratic flights that went to Winnie. But last year, we didn’t see as many scaup on Bowstring as we normally do – maybe about half.
“They weren’t that big raft of birds that came (in mid-October) and stayed until freeze-up,” he added. “That’s been the pattern since we started seeing dead birds.”
And it’s only been in more recent years – since about 2009 – that scaup have used Round Lake.
Officials also wonder about the link between spring migration and deaths in the fall.
“There’s some indication, just with the way the snail and parasite interaction works, that you need to have high use in the spring to have more snails infected in the fall,” Cordts said. “If that’s actually true, then we might not have many birds die this fall.”
The reason: delayed ice-out.
“This year, we think the scaup almost entirely overflew Winnie because it was ice-covered and the migration already had passed (when the ice went off the lake),” Loegering said. “So this could be a different scenario we are going to see this year.”