BOISE, Idaho (AP) — For the second consecutive year a large die-off of migrating geese has occurred in eastern Idaho, and officials say tests indicate poison put on agricultural fields to kill rodents is a possible cause.
The Idaho Department of Fish and Game earlier this week reported that about 335 migrating snow and Ross's geese died in March at Mud Lake and Market Lake Wildlife Management Areas.
Officials say tests on nine geese determined a form of phosphide caused the deaths. That product is used to coat seeds and in pellet form to kill voles.
About 2,200 geese died at the same two wildlife areas last year and officials initially attributed the deaths to avian cholera. But Fish and Game later said tests on 24 birds found that phosphide caused some of the deaths, while tests for avian cholera were inconclusive.
Still, state and federal officials are cautious about saying there's a direct link between the recent bird deaths and the use of poison on fields.
"When you get millions moving through on mass migrations, there are all kinds of things that could kill them," said Gregg Losinksi of Fish and Game.
The agency says tens of thousands of snow and Ross's geese during migration move through the wildlife areas in eastern Idaho that serve as rest stops in a desert area on one route along the Pacific Flyway.
The wildlife areas are also surrounded by agricultural fields where cyclic vole populations are thought to be peaking and can do extensive damage to crops.
"A surprising amount for animals that are so small," said Chanel Tewalt, spokeswoman for the Idaho State Department of Agriculture, noting that farmers have been expressing their concerns to the state agency.
Todd Grimm, director of Wildlife Services' Idaho operations, said a federal facility in eastern Idaho sells seeds coated with zinc phosphate that are intended to be placed in vole tunnels and paths.
"You want to reduce the non-target risk by doing that," Grimm said.
But he said a pellet form is also sold privately that is spread broadcast style.
The poison is inert but once ingested combines with moisture within the body to form lethal phosphine gas. That's what was found in the nine geese tested in the most recent die-off and some of the geese from last year's die-off.
Fish and Game officials in a statement about the most recent die-off said it's working with the state Agriculture Department and Wildlife Services to educate those who use the poison.
Tewalt and Grimm both noted that even when used within guidelines, there can be unintended consequences with non-targeted species.
Tewalt, while reiterating there wasn't a 100 percent link between the geese deaths and poison applications on fields, said the agency does work with farmers.
"We try to be proactive on the education side and make sure folks were aware of what happened last year and be extra cautious," she said.
Losinski said the number of geese deaths aren't a detriment to the population as a whole for either snow or Ross's geese, which he said number in the millions.
"For the most part, the major wave has gone through," he said of the geese that are migrating to breeding grounds in Alaska and Canada.
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