How A Mosquito-Borne Disease May Impact An Imperiled Idaho Species

Aug 28, 2017

The struggle to save the embattled greater sage grouse — while keeping the ground-dwelling bird off the Endangered Species List — has been going on for decades. Its population has plummeted from millions of birds to less than 500,000 in recent years.

Key to the fight is identifying and attacking what’s killing the bird, a challenge complicated by the fact that the threats vary depending on the state.

In Idaho, the Obama Administration’s Interior Department identified two main sources of population decline: wildfire and invasive species like cheatgrass. Both rip through the landscape at a ferocious pace, destroying or squeezing out the bird’s namesake food source (sagebrush). In other states, land uses like natural resource extraction and grazing are the bigger culprits.

Now – under the Trump Administration – Interior Secretary Ryan Zinke has added another threat to that list: West Nile Virus. During his visit to Boise in June, Zinke said he wanted to take the mosquito-borne disease into consideration as part of his sage grouse management strategy. In recommendations since that visit, he outlined changes to the previous administration’s plan that’s friendlier to mining and oil and gas companies.

But how much is West Nile virus (which we know can infect and kill people too) contributing to the decline of sage grouse?

EarthFix reporter Courtney Flatt looked into this question in Oregon. She went out into the state’s vast rangeland with a team of biologists who were there to trap and test mosquitoes for the virus, to get a sense of the problem.
 

The biologists say West Nile is endemic in Oregon. It was first detected around 2005 — and the next year saw a large die-off of sage grouse that had contracted the virus in the Jordan Valley. Since then, there haven’t been any other significant die-offs of sage grouse.

The West Nile virus is maintained through a cycle between birds and mosquitoes and depends on several factors to persist.

“A mosquito lands on an infected bird, it sucks blood, and then, depending on the viral load within that bird, they get West Nile virus,” Weidner said. “Then the mosquito lands on another bird, and that bird doesn’t have West Nile virus, and so they transmit it.”

It’s possible people are making the West Nile virus worse — by adding water sources to the desert. - EarthFix

But besides the 2005 die-off near at the southwest border of Idaho, the rate of infection is still unknown.

The scientists are working on a computer model to help predict West Nile virus among sage grouse – and how that impacts the chances of their survival.
 

Find reporter Frankie Barnhill on Twitter @FABarnhill

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