What's killing Idaho moose? In many cases, infestations of ticks and other parasites.

Nicole Blanchard, The Idaho Statesman on

Published in Outdoors

BOISE, Idaho — Nearly a year after launching a research effort to study why moose populations in Idaho have been declining, researchers with the Idaho Department of Fish and Game are starting to get some answers.

According to a Fish and Game news release, the agency partnered with researchers from the University of Idaho to attach radio tracking collars to 112 adult cow moose in early 2020 to study survival rates and causes of death. Across the country, moose populations have been declining since the 1990s, and moose biologists have told the Idaho Statesman in the past that there are likely several contributing factors — from increases in parasites that can prove fatal for moose to prevalence of old growth forests that aren't ideal moose habitat.

"We have seen the most severe declines in northern Idaho and southeast Idaho, but we don't know exactly why they are declining," Hollie Miyasaki, a moose biologist with Fish and Game, told the Statesman in July of 2019.

Researchers have now collected several months of data from the moose radio tracking collars, and the early results are already offering clues about moose survival. About 89% of the collared moose survived through the fall, Fish and Game reported.

"It really was a pleasant surprise," wildlife research manager Mark Hurley said in the news release. "We expected survival to be lower than that, given that moose populations are declining throughout the southern part of their range, including in Idaho."



Officials performed necropsies on the animals that died and found that more than half had died of parasites or disease. The majority of those deaths were due to emaciation from winter ticks, which are a species of external parasite that prefers to feed on species like moose, deer and elk. The ticks suck blood from the host animal, causing anemia and making it difficult for the host animal to maintain proper nutrition.

In 2019, Fish and Game moose biologist Kara Campbell told the Statesman more and more moose are facing massive infestations of winter ticks as climate change causes warmer seasons.

"High tick loads used to die off in the winter, but with warmer winters, we don't see tick die-off that we used to see," Campbell said. "So moose can accumulate ticks at high loads, up to 10,000 ticks per moose."

In February, a Vermont Fish and Wildlife Facebook post about winter tick infestations in moose went viral. Officials had found one animal with an estimated 90,000 ticks feeding on her.


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