Mule deer study raises red flags

Elsa Freise, Buffalo Bulletin via Wyoming News Exchange
Posted 7/1/21

There are still six months remaining in the three-year study to better understand why the population of the Upper Powder River mule deer herd is in decline, but already biologists have identified concerning trends.

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Mule deer study raises red flags


BUFFALO — There are still six months remaining in the three-year study to better understand why the population of the Upper Powder River mule deer herd is in decline, but already biologists have identified concerning trends.

Statewide, mule deer populations have been on the decline. Biologists have identified the Upper Powder River herd, which ranges in Hunt Areas 30, 32, 33, 163 and 169 south and west of Buffalo, as one of the high concerns.

“We just have way less deer than we used to," said Cheyenne

Stewart, the Sheridan Region wildlife coordinator for the Wyoming Game and Fish Department. “We were trying to look at what we are missing that could explain why the population isn't rebounding."

The Upper Powder River Mule Deer Initiative is also looking at history and strategies. Stewart said the initiative is pursuing answers to such questions as, "Are there differences in population metrics like survival and fawn recruitment for deer that migrate versus don't migrate?" and "What is the relation to agricultural areas versus native habitat?

Two years deep into the study, Stewart has identified some red flags.

“Overall poor body condition. When you compare these deer to the famous Wyoming-range deer that migrate record miles, our deer coming into winter (pre-winter) are comparable to their deer after they have been starving, at the end of winter (post-winter)," Stewart said. 

The energy required to lactate can contribute to poor body condition, but Stewart said that not enough does are lactating in December to explain the number of deer who enter winter in poor body condition. Stewart said there is some concern that low lactation rates among the herd's does could mean that fawns are at higher risk for winter mortality because of the lack of addition al nutrition.

Stewart has also identified high mortality rates primary causes of deaths including chronic wasting disease and mountain lion mortality  and a high CWD prevalence. 

"Even though it's a small sample size to make that calculation, (CWD prevalence) is higher than we would expect. Based

on the data we have now, we are sitting at the mid-teens (15 to 17 percent) for prevalence in harvested adult bucks. But this time next year, that can be changed a little bit," Stewart said. 

What's interesting about this project is that the doe prevalence for CWD is around 20 percent, higher than the adult buck prevalence an unusual occurrence. Game and Fish is curious to see if the adult buck deer prevalence increases, will the doe prevalence decrease, Stewart said.

Game and Fish has implemented several strategies aimed at boosting herd population: generating liberal licenses for animals that prey on deer, reducing doe harvest, treating the habitat to become more resilient to climate change to ensure that important mule deer habitats persist long-term, monitoring for CWD and other diseases and monitoring fawn survival (which has not been alarmingly low). Yet the trends have been consistent.

"Nothing can really explain what was really going on," Stewart said.

In phase one of the study, each deer selected for the three-year study was fitted with a GPS neck collar and various body measurements were taken. There are 70 running collars. If a deer dies over the course of the year, a new deer will be collared. The study has collared around 110 deer. Blood samples

were collected and will be analyzed for genetics. In addition, samples were collected to test for parasites, and a small sample of rectal tissue was collected to test for CWD. An ultrasound was also performed to assess body condition, Stewart said.

Every December, biologists catch the collared deer to take

the same body measurements. The Upper Powder River Mule Deer Initiative will end in December, with a final capture, the removal of all collars, recording measurements and additional CWD work, Stewart said.

This story is supported by a grant through Wyoming EPSCoR and the National Science Foundation.