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Movement matters for mule deer during the fall

Mule deer are on the move every fall and spring, and it’s imperative they have the best available food and least stress possible during the difficult travel.

10/9/2023 8:10:27 PM

Cheyenne - Most humans have a consistent address, living in the same location year-round. Although occasional moves happen, most people stick to one area for all seasons. But we all know someone who lives in a warmer location during the winter and returns to a more moderate climate as things start to heat up. It’s not a bad idea. Relocating over the seasons gives people the best weather at each locale.

The concept isn’t exclusive to humans. Many animals migrate to a different area as weather changes. But for deer, relocating seasonally isn’t for convenience or to chase the best weather; it’s a matter of life and death.

Change with the seasons

Rather than seeking warmer weather, mule deer relocate between summer and winter ranges for survival. They can’t go to the store to get their food. Instead, deer go where the food is, which can vary by season. Their summer range is lush with green grass and forage. During the winter, they typically travel to lower-elevation areas where they can find food with nutritional value.

Food in this seasonal habitat is only part of the equation. They need to have good groceries along the journey, too. To do this, deer “surf the green wave” in the spring — following grass as it grows.

“Deer usually move in blasts,” said Jill Randall, Wyoming Game and Fish Department statewide migration coordinator. “They’ll move several miles, then stop and hang out for a few days at locations with plenty of forage and to rest before the next move. These stopover areas are very important for deer to gain nutrition during migration.”

In the fall, deer begin to move to their winter range. Like surfing the green wave, deer in the fall race against the “brown down” — trying to stay one step ahead of the drying vegetation to get the last bit of nutritional greens along the way. The path they take is nearly identical to their spring migration.

Although some of Wyoming’s mule deer make long-distance migrations, some remain residents of the same area year-round. They instead move along elevation changes rather than putting in the miles. No matter the distance traveled, it’s important for deer to have suitable habitat and food sources for the duration of the trip.

“Within a herd, having these different strategies can help the population during challenging conditions like winter or with changes to the landscape,” said Embere Hall, supervisor for the Game and Fish science, research and analytical support unit.  “It’s important to maintain all of these options for a population and give deer the best chance of survival.”

Deer stay faithful to their migration routes. Most deer stick to their set path and travel the same routes each migration.

“They learn from mom where to go, and most of those deer will do the same things mom showed them,” Randall said. “They summer in the same vicinity in family groups then go to winter in the same vicinity as the previous year.”

Once deer arrive in their seasonal range, they have to have good habitat to fill their needs. In the summer, this means they need plenty of green grass and nutritionally dense foods to pack on the fat before the snow flies.

Habitat is important on winter range, too. While food is sparse, having sources like sagebrush can help get deer through the winter. Migrating deer usually head to lower elevations where snow is shallow and they can move around without exerting as much energy and burning much-needed fat stores. 

Muleys on the move

Some of the most significant projects for mule deer in recent years have taken place where deer and people intersect. As deer hoof it over land, people drive the state’s roads. It’s no surprise that sometimes these travelers cross paths, and it’s often fatal for deer.

According to a 2021 report released by The Nature Conservancy titled, Impacts of Roadways on Wildlife in Wyoming, about 5,500 mule deer are struck by vehicles in Wyoming each year. These collisions are vastly underreported, and a conservative estimate is two times as many deer are hit on Wyoming’s roadways each year. That means 1.5 percent to 3 percent of Wyoming’s deer are lost annually on the state's roads. Reducing these incidents is imperative for human safety and to maintain healthy deer populations.

Wildlife overpasses and underpasses are employed to reduce these types of collisions. Some overpasses and underpasses are put at roadways along migration routes, providing key connectivity between summer and winter ranges. Others are placed within a particular seasonal range, providing deer with safer access to a larger area without the risk of crossing a road.

Wildlife crossings aren’t the only way to help migrating mule deer. Game and Fish and partners work throughout the state to improve habitat for deer. Habitat improvements can include thinning conifers that encroach on sagebrush and other food sources, treatments to reduce wildfire threats, weed reduction treatments and spraying to reduce invasive grasses like cheatgrass. By focusing on habitat, wildlife managers can increase food sources for mule deer and ensure they have the best chance of survival. 

Ensuring fences are more passable is another way to help deer on the move. Fences are necessary for many land uses, especially agriculture. But some fences can create hazards for migrating mule deer due to the type of wire or height. Some fences aren’t passable by deer; others bottleneck movements, slow travel or can ensnare deer attempting to jump over them. However, wildlife-friendly fencing and gates that can be left open seasonally can reduce these impacts while still serving the needs of landowners.

Wildlife-friendly fencing includes a smooth bottom wire of a fence placed 18 inches or more from the ground for wildlife to crawl underneath, a top wire or pole no taller than 40 inches to facilitate jumping and proper spacing of wires so legs don’t become entangled when animals jump the fence. This style of fencing still marks boundaries and contains livestock without stopping deer.

Converting fencing and adding gates is one of many things landowners do to help migrating mule deer. Reducing weeds or invasive grasses like cheatgrass is another immensely useful thing to help migrating animals. Reducing weeds provides better-quality forage not only for wildlife but for livestock as well. Programs are in place to help landowners maintain healthy habitat. For example, the USDA’s Grassland Conservation Reserve Program pays landowners an annual habitat lease for keeping grasslands intact while grazing livestock.

By reducing human impacts on migratory wildlife and their habitat, landowners can continue to significantly help facilitate deer movement in Wyoming.

Even the most minor actions can make a big difference in helping mule deer migration. Whether slowing down and watching for deer on Wyoming’s highways, donating to habitat or roadway projects, converting fencing or helping with on-the-ground efforts, we all can make a difference.

Following a few simple steps can prevent many wildlife collisions:                         

  • Slow Down
  • Expect wildlife and scan the sides of the roads.
  • Use headlights and stay alert while driving at dusk, dawn and at night
  • If you see one elk, deer, or antelope by the road, expect there to be more nearby.
  • If an animal is on the road, expect the unexpected. They do not instinctively know how to react to your car.
  • If you encounter an animal crossing the road, switch your headlights to low beam so that they are not blinded and can move out of your way.
  • Give the animal time and room to move off the road. Do not try to outrun it.
  • If you see a wildlife-crossing sign, pay attention. It is there for a reason.
  • Do not swerve to miss an animal. Steer toward the animal's hindquarters, as they most often will move forward.

Nationwide, more than 150 people are killed and 29,000 injured each year in animal/vehicle collisions. If you see an injured deer, call the nearest Game and Fish office with specific information about the location (road, mile-marker, etc.).

This story, written by Wyoming Game and Fish Department staff, originally appeared in the September 2023 special mule deer edition of Wyoming Wildlife magazine.

(Breanna Ball, Public Information Officer - (

- WGFD -