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Poisonous gas kills hundreds of geese in eastern Idaho


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The recent die-off of more than 300 snow geese and Ross’ geese in eastern Idaho won’t impact the overall population estimated at 2 million. | Kris Millgate, Tight Line Media

JEFFERSON COUNTY — Poisonous gas caused the deaths of more than 300 snow geese migrating through eastern Idaho in March, the Idaho Department of Fish and Game says.

The Idaho Fish and Game Wildlife Lab and the Washington Animal Disease Diagnostic Lab found traces of phosphine gas in tissue samples from dead birds collected at Mud Lake and Market Lake wildlife management areas.

Market Lake WMA hosts a blizzard of feathers in the spring. About 50,000 big, bright-white and honking snow geese stop at ponds near Roberts to rest and refuel, but for the second year in a row, some of those geese died. The trend warranted testing even though the overall snow goose and Ross’ goose population, estimated at 2 million, is not impacted by the die-off.


Thousands of snow geese stop at Market Lake Wildlife Management Area during spring migration. Several hundred have died due to poisonous gas in the last two years while resting in eastern Idaho. | Kris Millgate, Tight Line Media

“It won’t cause any population concerns with those species, but it does raise concerns with other birds that are not as visible — birds like partridge, pheasant and Canada geese that are not as easy to find,” said Jeff Knetter, Fish and Game upland game and migratory bird coordinator.

During the same two-year die-off, the vole population in the area increased. Voles are similar to mice in size, and farmers often use zinc phosphide to control the rodents in their fields. When phosphide is consumed, it turns into the poisonous gas phosphine.

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“Ag does use zinc phosphide to kill voles, but in truth we’re not sure where the geese picked it up,” Knetter says. “The folks that are using zinc phosphide are just trying to deal with voles damaging their crops. We can’t make a link at this point, but we want to provide people with resources so they can educate themselves on the issues.”

Outdoor journalist Kris Millgate is based in Idaho Falls, Idaho. See her work at