Invasive Snails Take a Toll on Native Ducks : NPR

• by Sea Stachura

• The number of lesser scaup ducks is dwindling, and it could be an invasive species that does them in. Invasive snails and parasites are attacking these and other ducks on the Upper Mississippi.

• All Things Considered, May 26, 2008 ·

• Nearly 150 invasive species live in the Mississippi River Basin, and while not all of them are destructive to native habitat, this snail has become a duck killer: The snail has helped kill nearly 50,000 ducks in the last few years in the Upper Mississippi Wildlife Refuge, which borders Wisconsin, Minnesota and Iowa.

• The area is a rest stop of sorts for more than 450,000 migrating ducks every year, which snack on wild rice and snails.

• Three types of invasive intestinal parasites are killing the birds.

  “All three use an invasive snail, called the mud byfnia, or faucet snail, as an intermediate host,” said Jim Nissen, who works for the Fish and Wildlife Service.

• Nissen says when the ducks eat these snails, the parasites they carry bore into the ducks’ intestinal walls.

  “They gorge on blood and then lay eggs,” Nissen said. “The eggs are passed through the birds’ feces, and that’s how they reach the snails. That’s how the cycle is perpetuated.”

  The lesser scaup duck is particularly susceptible to this parasite, killing them only in a few days. Their bodies litter the water like decoys. There were eight million lesser scaup in North America in the late 1970s now their numbers have dropped by half. Nissen worries that this snail-parasite duo could spell the end of the lesser scaup.