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Pronghorn fawn survival in Montana plummets amid record summer drought

Pronghorns captured and fitted with GPS collars in northern Montana and Canada have provided a wealth of data for wildlife biologists. The most recent study details what habitat the animals seek out during their spring and fall migrations.  (Courtesy of Brett French/Billings Gazette)
Pronghorns captured and fitted with GPS collars in northern Montana and Canada have provided a wealth of data for wildlife biologists. The most recent study details what habitat the animals seek out during their spring and fall migrations. (Courtesy of Brett French/Billings Gazette)
By Brett French Billings Gazette

BILLINGS – Montana’s long, hot summer has taken a toll on pronghorn fawns, dropping survival rates to a record low in several areas.

“Overall, the numbers in Region 7 dropped pretty significantly – 39% regionwide,” said Ryan DeVore, a Fish, Wildlife & Parks biologist based in Broadus. “It hit us pretty hard.”

Region 7 covers a large swath of southeastern Montana.

Farther west in Region 5, FWP wildlife biologist Justin Paugh is seeing similar pronghorn problems based on July surveys. Across the region, fawn-to-doe ratios averaged 43 fawns per 100 does. That compares to a long-term average, dating back to 1983, of 60 fawns per 100 does. Prior to a blue-tongue outbreak in 2007, the numbers were even better, averaging 70 fawns per 100 does.

“It’s like the scale shifted and the fawn-to-doe ratio has declined ever since” the disease, Paugh said.

Blue-tongue outbreaks are known to affect doe fertility, he added, but biologists expected to see the fawn ratio creep back up as infected animals died off and were replaced by new females. Pronghorns live about seven to 10 years.

In Region 7, this summer’s count revealed two trend areas with 40 fawns per 100 does in areas that in the past saw counts as high as 90 fawns, DeVore said. Some survey areas in Region 6, in northeastern Montana, fared even worse with fawn ratios as low as 20 to 30 per 100 does.

“It’s in those areas where drought is more predominant,” said Scott Thompson, Region 6 wildlife manager, mainly near Glasgow and Malta.

In areas that saw more moisture, such as Hunting Districts 650 and 670, fawn numbers ranged from 60 to 70 per 100 does.

Drought

Low fawn survival may be blamed on poor forage conditions this spring and summer, the biologists speculated.

A mild winter meant most pronghorn does went into the spring birthing season in pretty good physical condition. By the time fawns were born, however, the country was already drying out leaving less to eat and reducing hiding cover for the fawns to avoid predators like coyotes, eagles and lions.

This summer’s drought conditions could also result in lower fawn production next year. It all depends on whether this fall is wet enough to provide some green growth across the state, providing pronghorns with good forage before winter hits. Right now, their body condition isn’t great.

“We need moisture,” Paugh said.

“If we have an average winter we could see some higher than normal over-winter mortality in does and fawns,” he added.

“This is going to affect us for the near future, as well,” DeVore said. “It’s a long cycle, so time will tell how bad it gets.”

Region 6 biologists know something about long pronghorn cycles. After the population nosedived following the severe winter of 2011 and disease outbreaks, pronghorn numbers have slowly but steadily climbed, in part due to a restriction on hunting tags.

“Last year we finally saw average population levels in some areas,” Thompson said. “So it’s kind of hit an average and plateaued. We’re not seeing fawns contributing to the population.”

Southeast

Southeastern Montana had seen record high pronghorn numbers in the Broadus and Alzada areas, prompting FWP to offer extra permits to thin burgeoning herds – partly due to landowner complaints, but also to find a biological balance, DeVore said.

Last season, hunters killed more than 2,200 pronghorns in Hunting District 705 in the southeast corner of the state, the most of any hunting district. That compares to more than 2,500 killed in all of Region 3 and 2,800 in Region 5. Region 7’s total pronghorn harvest hit 6,500 compared to 2,100 in Region 6.

Statewide, more than 16,100 pronghorns were taken by hunters in 2020. That was up from 2019 when more than 13,100 pronghorns were killed.

“Those that hold tags should have a good season,” Thompson said, noting that buck ratios remain strong in the northeast.

Habitat

The drought also led animals to leave large swaths of country empty in favor of areas within 2-3 miles of water.

“There are several miles of country with nothing in it,” Paugh said.

DeVore said hunters may have to search more to find animals this season, since they may not be in areas they’ve traditionally occupied in the past.

The early archery season for 900 series tags opened on Aug. 15.

The general archery season opened Saturday with the pronghorn rifle season starting on Oct. 9.

Thompson said he would be remiss if he didn’t remind hunters to be extra careful this year about avoiding fire starts. That means avoiding parking in tall grass and carrying a fire extinguisher or shovel and bucket.

“Every landowner I’ve talked to is concerned,” he said.

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