Wyoming Game and Fish Monitor Winter Mortality of Wildlife

Wyoming Game and Fish Monitoring Winter Mortality of Wildlife – And There’s A Lot

Written by on March 7, 2023

Data collected from mule deer herds across Wyoming tell a tragic story – young animals dying and adults struggling to forage through deep, hard snowdrifts as a harsh winter continues.

Much of Wyoming is experiencing an increase in snowfall and frigid temperatures this winter. As a result, wildlife managers across the state are actively monitoring the impact on Wyoming’s wildlife. Unfortunately, the managers are seeing increased mortality in some areas of the state.

“Wyoming is used to tough winters, but it has been a while since we have had a winter where severe conditions were so widespread across the state,” said Doug Brimeyer, Wyoming Game and Fish Department deputy chief of wildlife. “Wildlife managers throughout the state are acutely aware of the effects winter has on big game populations.”

Harsh winters are not uncommon in the West. Wyoming’s big game has faced difficult winter conditions, most recently in 2017. Game and Fish wildlife managers will incorporate winter severity and mortality as they formulate hunting season recommendations for the 2023 seasons.

“Game and Fish has a proven track record of adaptively managing the state’s wildlife through setting hunting seasons that take into account the challenging conditions wildlife face in the winter,” Brimeyer said. “The public is encouraged to attend their regional season-setting meetings to learn more about winter loss in their areas.”

Mule deer foraging in deep snow

Courtesy Wyoming Game and Fish

One of the biggest concerns is public safety as some big game herds cross roads and highways as they move to lower elevations and habitats in search of forage.

Research shows that slowing down by just five miles per hour can significantly increase a driver’s reaction time to avoid a wildlife-vehicle collision.

Across the state, reports detail early-winter impacts on big game, but much of the winter season’s outcome still remains to be seen. Wildlife managers will have a better understanding of winter impacts and mortality in the coming months.

Casper Region

The Casper Region is experiencing moderate winter conditions in the northeastern portion of the region in Thunder Basin and the Black Hills. In these areas, deer and pronghorn populations will likely experience normal winter survival as snowpack and temperatures have been moderate. However, much of the rest of the region is experiencing relatively harsh winter conditions.

Areas around Lusk, Pine Ridge north of Casper/Glenrock, northern Laramie Range, southern Bighorns, Rattlesnakes, and low-elevation basin areas are experiencing heavier than normal snowpack. Unlike most winters in the Casper Region, snow has persisted on the landscape for the past three months, with the exception of some wind-blown areas.

In particular, mule deer and pronghorn in the Casper and Glenrock areas have the highest potential for above-normal winter mortality, but this will depend on how the March weather unfolds. Currently, it appears collared deer and pronghorn are experiencing normal winter survival south of Casper in the Bates Hole area despite higher-than-normal snowpack and prolonged cold temperatures.

While the Casper Region still expects somewhat higher than normal deer and pronghorn losses in some areas, this will heavily depend on weather conditions throughout March and early April.

Cody Region

Winter severity varies widely in the Bighorn Basin, with conditions milder in the north and more persistent snow cover occurring in the southern portion of the basin. On the west slope of the Bighorns, conditions have been colder and snowier than average and lower-elevation winter ranges have been covered in snow since early winter. South-facing slopes are slowly beginning to open up, but this is only true of areas below 7,000 feet. Despite the persistent snow and cold snaps, mule deer survival has been relatively good so far in the Worland and Greybull districts. However, wildlife managers expect to see deer mortality peak in April and May, as it has in previous years.

The northern portion of the Bighorn Basin has experienced a relatively mild winter, with the winter range experiencing periodic sub-zero temperatures and low levels of snowfall. Game and Fish biologists anticipate deer survival could be higher than normal if the area does not receive high amounts of spring snow.

Green River Region

An early onset of winter coupled with continuous snow storms and below-zero temperatures has resulted in severe winter conditions in most of the Green River Region. Snow depths range from 1 to 3 feet deep across lower elevations with some snow drifts several feet in depth. The Red Desert area has been hit extremely hard with heavy snow and wind resulting in deep, crusted, and drifted snow.

Big game in this area are moving long distances in search of food and relief from the deep snow. As a result, many big game animals have died and wildlife managers expect winter mortality to continue for the next few weeks.

The movement of big game animals to more accessible habitats has been especially evident with elk in places where they haven’t been seen in many years. Due to the increase in damage by the elk and the risk of co-mingling with livestock, Game and Fish officials have initiated emergency supplemental elk feedings in the Cokeville and Kemmerer areas.

Jackson/Pinedale Regions

These regions experienced an early onset of winter beginning in late October with about average snowfall to date in the mountains, but above-average snow levels on lower-elevation winter ranges and consistently colder than normal temperatures. Wildlife managers can access near real-time mortality information through GPS-collared animals, which currently show greater than 50 percent mortality of collared mule deer fawns in the Wyoming Range herd. Collared adults in the Wyoming Range and Sublette deer herds are experiencing average mortality.

Juvenile mortality typically averages about 25 percent in these herds. When inspected nearly all of the mortalities were found to have gelatinous bone marrow signifying malnutrition. By all accounts, managers are expecting to see above-average mortality for both mule deer and pronghorn. However, an accurate assessment of loss won’t be known until later this spring as many animals, particularly adults, won’t succumb to winter until April or May.

The larger ungulates such as elk and moose aren’t typically as affected by winter compared to pronghorn and mule deer, and will likely experience average mortality. However, wildlife managers are responding to an increased number of elk causing damage on private lands as they seek forage at livestock feeding operations. Due to the increase in damage by the elk and the risk of co-mingling with livestock, Game and Fish officials have initiated emergency supplemental elk feeding in Star Valley.

Lander Region

Winter severity throughout most of the Lander Region has been extreme, with sub-zero temperatures, high winds and record snowfall producing deep-crusted snow cover across the region. The exception is the Dubois area where the winter is not as severe. The winters of 1983 and 1992 are memorable as far as severity, and this winter is at a minimum on par with those years — if not worse. The Rawlins area is, by some data sets and accounts, worse than the winter of 1949 with regard to snow accumulation and cold temperatures.

To help illustrate the impact winter conditions are having on wildlife, 33 adult doe pronghorn in the Red Desert herd were still collared and alive at the end of December 2022. Movements recorded from these animals show extreme migrations, often outside the herd unit. During the past eight weeks of severe weather and deep snowfall, 14 of these 33 collared, adult does have died.

Wildlife biologists are expecting more pronghorn to succumb to starvation and exposure. In addition, wildlife biologists are responding to calls concerning dead elk that have been hit on the interstate and railroad corridors as they try to move to more accessible habitats.

Laramie Region

Winter severity throughout the Laramie Region is variable depending on the location and timing of winter storm events. Winter conditions in the Laramie Valley are minimal and the east slopes of the Snowy Range are at average snow levels. North-facing slopes contain forage and many east and south-facing slopes are mostly open. Snow conditions in the Laramie Mountains are average to above average.

Wind events have opened up slopes to allow ungulates to browse and eat critical shrub species needed to meet their dietary needs for survival. The majority of winter loss in this area has been juvenile deer.

Winter conditions in the Platte Valley are average to severe. The western slopes of the Snowy Range and the entire Sierra Madre Range have well above-average snow levels. Above-average snowpack levels will be crucial for spring runoff and increased plant production necessary to meet the dietary needs for lactating ungulates.

Sheridan Region

Overall, winter conditions in the Sheridan Region are more severe this year than in the past several. Near Kaycee and Buffalo there are open slopes where snow has melted on warm days, but most of the region is experiencing persistent snow cover. In most areas of the region, significant snow cover has been in place since November, particularly east of Sheridan and Buffalo. Snow water equivalents in the Tongue and Powder river drainages at the end of February were 118% of the median amount.

The deep and hard-crusted snow in this region makes it difficult for animals to dig through. Wildlife biologists and game wardens have started receiving calls from concerned members of the public and landowners reporting dead animals, particularly fawn deer, along with animals that are alive but are weak and in poor body condition.

Game and Fish wildlife managers will continue monitoring winter conditions across the state. Wildlife managers encourage the public to help wintering wildlife by:

  • Avoid disturbing wildlife during this critical time. During the winter wildlife survive on a diet lower in nutrition and will migrate to lower elevations where the habitat is better, more available, and contains less disturbance to avoid burning unnecessary calories.
  • Resist the urge to feed wildlife to help them through the winter. It is natural for people to feel compassion for struggling wildlife, but feeding can result in increased disease transmission and do more harm than good. Deer in particular have specialized digestive systems that are not adapted to hay, apples or corn.
  • Leaving gates open where possible to allow unimpaired movement of animals across the landscape, especially along roadways, may reduce potential wildlife-vehicle collisions. This also can help reduce damage to fences and prevent animals from getting entangled and dying. Many landowners have modified their fences to make them more wildlife-friendly by replacing the bottom wire with a smooth wire and lowering the top wire or adding a pole to the top.
  • Avoid snowmobiling or recreating on low-elevation winter ranges. Opt for the high country with deeper snow where animals are less likely to be found.
  • Motorists should plan to drive slower and pay close attention to animals along our roadways. Wildlife-vehicle collisions occur at a higher rate during the winter months. Research has shown that slowing down, even just five miles per hour can greatly increase a driver’s reaction time to avoid a collision. This is especially important at dawn and dusk when animals are more active and harder to see.

Methods to preserve some animals are not practical for others. For example, struggling elk herds are getting additional sustenance from emergency feedings of hay, to prevent them from mingling with domestic livestock.

However, mule deer are unable to digest hay, corn, and most other foods that are not part of their natural diet. Wyoming Game and Fish actively discourages feeding mule deer in winter. Despite good intentions, deer can easily die with full stomachs of food they are unable to digest.

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