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Research links grouse population declines to West Nile virus

JOHN McCOY | Gazette-Mail
Ruffed grouse populations have declined in West Virginia, and recent research done in Pennsylvania indicates that West Nile virus may at least be partly to blame. The research shows a correlation between West Nile outbreaks and dips in the Keystone State’s grouse population.

West Virginia’s ruffed grouse populations have declined dramatically since the 1950s, ‘60s and ‘70s.

Biologists place most of the blame on loss of prime habitat, but research taking place in Pennsylvania has identified another potential culprit — disease. Studies have linked declines in Keystone State grouse populations with outbreaks of West Nile virus.

Lisa Williams, the Pennsylvania Game Commission’s program leader for grouse and webless migratory game birds, said the research sprang from hunters’ concerns.

“I was talking to a fellow who hunted in northeastern Pennsylvania,” she recalled. “He had kept very careful records of his hunts. He told me that sometime around the year 2000, things started to change.

“I told him that it was a habitat problem — that grouse populations decline after [young forest] habitat grows into mature forest. He pounded his fist on the table and said, ‘Listen to me. I’m telling you something is happening.’”

Spurred by the hunter’s passion, Williams started looking at 50 years’ worth of data the PGC had gathered from hunters who participated in the state’s grouse cooperators’ program.

“We get data from about 300 hunters a year, so we have this great data set,” Williams said. “When I looked at the data, I came to the conclusion that something changed in the early 2000s.”

Up to then, she explained, grouse populations had risen and fallen on a fairly predictable 7-year cycle.

“After 2000, that changed,” she added. “We’d have a [population] crash, then an anemic recovery, then another crash. We never got another boom like we had in the past.”

Williams looked at data from other states. They all showed the same trend: a population dip followed by a piddling recovery.

“I started wondering what could change that quickly, and across that large a geographic area,” she said. “The answer I came up with was disease. Once I started thinking along those lines, I began looking at diseases that hit in the early 2000s. I immediately thought of West Nile. I knew it affected crows, blue jays and sage grouse, so I started looking to see if it affected ruffed grouse, too.”

In 2014, Williams put together a study of the virus’ effects on newly hatched grouse.

“We collected grouse eggs from the wild, and we sent them to a grouse propagator in Idaho,” she said. “He had a quarantined facility, so we knew the poults wouldn’t get bitten by mosquitoes infected with West Nile.

“After the eggs hatched, he sent us back 4- to 6-week old chicks. Once we got them settled in here, we introduced them to the virus and waited to see what would happen. Forty percent of them died within a week. Following protocol, we euthanized the rest and performed necropsies on them. An additional 50 percent had significant organ damage, particularly to the heart and brain.”

Based on those results, Williams and her colleagues estimated that 40 to 70 percent of birds infected in the wild would not survive.

The next phase of the study took place during the 2015-16 and 2016-17 grouse seasons. Williams had grouse hunters collect blood samples from birds they killed.

“The first year, we found that 13 percent of the birds had been exposed and had survived,” she said. “In the second year, 23 percent were survivors.”

The researchers found that more birds survived the virus if they lived in good grouse habitat. In the state’s southern counties, which have poorer habitat, fewer birds survived.

In a parallel project, biologists trapped mosquitoes from woodland settings to see how many were potential West Nile carriers.

“In six days in June, we caught 8,500 mosquitoes,” Williams said. “There were 24 species, which blew everyone away. Of those, eight of those carry the virus and are known to bite birds.”

When Williams looked for relationships between West Nile prevalence and declines in grouse flush rates and brood counts, she found a 50 to 70 percent correlation.

“That was really surprising,” she said.

Since those studies were conducted, researchers at Penn State University have taken grouse data collected for the state’s Breeding Bird Atlas, and have computer-modeled those data taking West Nile prevalence and habitat quality into consideration.

“They found that West Nile and habitat act together,” Williams said. “But they found that West Nile was the driving factor. The study was tight enough to be accepted for publication, and will be published in the Journal of Wildlife Management.”

Studies relevant to one state are not necessarily relevant in another, and West Virginia’s grouse project leader isn’t yet ready to blame the Mountain State’s grouse declines on the disease.

“I think it potentially could be affecting grouse numbers,” said Mike Peters, a biologist with the West Virginia Division of Natural Resources.

He said there’s too little data from the state’s grouse-survey cooperators to draw any conclusions about West Nile.

“We only have 28 cooperators a year if we’re lucky,” he explained. “So if we try to correlate [a decline in flush rates] with the time when West Nile came along, the data we have don’t tell us a lot.”

Williams and her colleagues’ West Nile research seems to have convinced Pennsylvania officials that their grouse season might be too long. This year, they closed the state’s post-Christmas “late season” in an attempt to boost survival.

Peters said there isn’t yet enough state-specific evidence to shorten West Virginia’s season.

“We’re not at a point where we need to do that,” he added. “But [the Pennsylvania research] does raise a question that should be looked at.”

Since there’s not much chance that West Nile virus can be eliminated, Williams believes states should concentrate on creating ideal grouse habitat.

“I’d say the best thing we could do would be to double down, triple down on habitat,” she said. “We need to get away from this idea that tree-cutting is bad. We have a whole bunch of species that rely on young-forest habitat, and those species are in trouble. Landowners need to get away from high-grading their timber and consider taking out patches of forest, not just individual trees.

“We have a gorilla in the room in West Nile virus. The best way to stack the deck in the grouse’s favor is to have better habitat.”

Contact John McCoy at, 304-348-1231 or follow @GazMailOutdoors on Twitter.

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