Wednesday, February 8th, 2023
Wednesday, February 8th, 2023

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Is West Nile virus decimating grouse?

Harrisburg — It’s a tale often told and retold: grouse population declines are the result of changing habitat. Simply put, there’s not as much scrubby stuff as their once was, and bird populations have declined as a result.

That’s all true, biologists say.

But now they’re wondering if there’s something else in play. Specifically, is West Nile virus doing damage to the birds?

Pennsylvania Game Commission biologists are trying to find out. In fact, they’re already doing or planning several studies looking at birds and bird hunters right now.

Ian Gregg, who heads up the commission’s game bird section, said that the grouse population seemed to begin its decline at about the same time West Nile showed up on the landscape. It’s possible that was just dumb luck, he said.

“But there is some evidence that West Nile can be devastating to captive grouse populations,” Gregg said.

They’re not the only birds impacted by the pathogen, and maybe not even the most susceptible to its effects.

“Recent laboratory tests have shown that West Nile is 100 percent lethal to crows, but the mortality rate is likely to vary among susceptible species,” according to the American Bird Conservancy.
“Historically, immunologically naive birds have suffered devastating population losses due to introduced disease in many parts of the world. In the end, there may be very little that wildlife and health officials can do to contain the spread of West Nile virus in the U.S. to protect birds.”

Scientists want to try, though, and not just here. There’s enough concern that several groups are studying the issue. The U.S. Geological Service National Wildlife Health Service is coordinating some research looking at West Nile and grouse, too.

The commission’s study began last year and will continue through 2016.

In the meantime, the commission is also trying to figure out just what kind of grouse it is that hunters are harvesting here.

It’s been asking hunters to submit tail and rump feathers from birds they’ve shot. The goal is to compare the percentage of adult birds in the harvest to juveniles.

Under good conditions, adult birds will be a minority of the harvest, wrote commission grouse biologist Lisa Williams in a letter to cooperating grouse hunters going into the fall 2014 seasons. During the “good old days” of high grouse populations in the 1970s and 1980s, she wrote, hunters were taking anywhere from 2.75 to 4.55 juvenile grouse for every one adult bird.

In the 2013-14 season, by comparison, the ratio of adults to juveniles in the harvest was one-to-one.

“Since adult grouse are typically the most successful breeders, the finding that adults accounted for a full 50 percent of the 2013-14 samples is another reason for concern,” Williams wrote.

It could be that grouse are having less success breeding and producing fewer young, or that fewer young birds are surviving to fall, she said. Weather, predators and other factors could also be in play.

Those are all questions the commission is attempting to answer, she said.

Finally, the commission is going to look at its grouse – and woodcock – hunters. It will survey a random sample of grouse and woodcock hunters this spring to find out where, when and how often they hunt, what they experience, and what they think of it all, Gregg said.

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