Western Working Lands Snapshot: Migratory Big Game

What Are Migratory Big Game?

Migratory big game are large, native mammals that are popular with wildlife watchers and hunters. The West’s big game species include elk, deer, pronghorn, moose, and bighorn sheep.

These animals travel across the landscape in search of food. Herds of migratory big game are emblems and economic drivers of the American West.

Why Do These Animals Migrate?

Migrating between the West’s mountains and valleys in concert with the seasons allows these animals to access the best, most nutritious food throughout the year while escaping harsh conditions such as deep winter snow or summer drought. 

Big game are herbivores that eat grasses, wildflowers and shrubs. These plants are most nutritious in early spring when the leaves are small and have less fiber. Spring comes first at low elevations, and then slowly progresses upward in elevation. Big game follow this ‘wave’ of newly emerging green plants each spring. By ‘surfing the green wave’, these mammals can eat more plants when they are most nutritious. 

By the time summer heat dries out plants at lower elevations, migratory big game are high in the mountains where green plants are still abundant. When the snow begins to fall in autumn, big game slowly move back down to graze at lower elevations where winter isn’t as severe.

If big game cannot migrate away from harsh winter conditions at higher elevations, individuals will perish, and the herd dwindles.

How Do Big Game Benefit Us?

Big game are important components of the ecosystem and our economy. They provide food for carnivores like bears, as well as scavengers like eagles and coyotes. Migratory big game also influence plant communities by fertilizing soil and dispersing seeds through their feces. 

Humans have relied on big game for their meat and hides for millennia, even following or living along migration paths to harvest these mammals. Today, big game herds contribute about $1 billion each year to the national economy through hunting and tourism. In western states like Montana and Wyoming, wildlife-related tourism and hunting are among the top income generators.

When big game are free to migrate, the landscape can support a larger, healthier population of these animals. For instance, when herds move frequently, plants have time to recover and re-grow, particularly on winter range. This benefits ranchers’ livestock, as well as wildlife that rely on rangeland plants for food.

How Far Do They Migrate?

Migrations can be as short as a few miles, but some mule deer have been clocked migrating over 150 miles! Both pronghorn and elk can also migrate over 100 miles. 

Some big game complete their season journey in just a couple of days. Others may travel for up to three months, lingering along the way to eat newly emerging plants. Shorter distance migrations, like those of bighorn sheep, can still be impressive, as they often include large elevation changes up or down steep mountains. 

How Do Big Game Know The Way?

Migratory big game are excellent navigators with strong spatial memories. Both individuals and herds can remember where they have traveled in the past, as well as the most efficient route to return to these places. 

Migration knowledge is likely passed on from mothers to their young. Big game babies are born in the spring or early summer and follow their mothers from summer to winter range during their first migration.

Since most big game are social and move in herds, individuals can also make small adjustments to their migration routes based on the herd’s collective decisions.

What Threatens Migratory Big Game?

Like most wildlife, the biggest peril facing big game in the West is habitat loss. Migratory animals require particularly large swaths of intact, connected open space to thrive. When their migration pathways are blocked or disappear, big game suffer.

Development: Everyone wants a piece of paradise! The beautiful, wide-open landscapes that support migratory herds are also places where people want to live. Housing demand has increased exponentially in many western states, which threatens habitat for big game. Other types of development like oil and gas wells, new access roads, and large-scale solar energy arrays also impact migratory big game.

Roads and Fences: Human-made linear structures crisscross migration corridors, creating obstacles for migratory big game. Roads take a deadly toll, killing an estimated 1-2 million large animals each year nationally. Fences can also kill or injure big game. Big game must navigate dozens of fences each time they migrate, sometimes getting tangled or trapped when fences are not wildlife-friendly. Fences are especially hard on pronghorn because these animals don’t jump over them but prefer to crawl under. 

Habitat Degradation: Weeds like cheatgrass and other invasive annual grasses are taking over rangeland throughout the West. These invasive grasses outcompete native plants, leaving less nutritious food for big game because cheatgrass and other weeds green up earlier and die sooner than native plants. Trees are also expanding into previously wide-open rangelands, replacing the nutritious native plants that big game rely on.

Can We Conserve Migration Pathways?

Yes! Scientists have tracked thousands of animals to identify their migration routes. By mapping these pathways, we can see when and where big game are moving.

Migration maps also show us pinch points that restrict the animals’ journeys, along with areas they avoid during migration. Equipped with this information, public and private partners can identify solutions to help big game and prioritize places to conserve their habitat.

Some of these solutions include: 

• Local plans or guidelines that cluster housing or energy development outside of known migration routes. 
• Financial assistance for landowners who keep large ranches intact and migration pathways open and connected. This includes conservation easements, habitat leasing, and rangeland improvements (such as fostering healthy native plants and removing weeds) that benefit both livestock and big game. 
• Building over or underpasses that help big game and other wildlife safely cross highways.
• Modifying fences to be friendlier, removing them altogether, and not building new fences in known pathways will ease the stress on migrating big game. Some ranchers are trying out GPS collars that manage livestock virtually, allowing old fences to be removed. Additionally, avoiding building new fences in key migration pathways benefits migratory big game. New and ever-expanding resources can help landowners and managers know where migration routes are and where to avoid creating obstacles (see below). 

Do Private Landowners Play A Role?

Private working lands—especially large, intact agricultural ranches—are the key to maintaining healthy herds of big game into the future. Migrating animals can’t see “private” or “public” property lines and travel regularly between both. For instance, many of the thousands of elk that graze that in Yellowstone National Park during the summer spend a lot of the winter grazing on low-elevation private lands. 

Landowners who voluntarily conserve large tracts of open space are very important for maintaining the West’s emblematic herds. Keeping ranches in operation is one of the best ways to maintain migration routes for big game. Western landowners are also helping big game by making their fences friendlier for migrating animals, carefully managing grassland pastures, and controlling the spread of weeds like cheatgrass. But all these stewardship actions cost money!

WLFW’s Migratory Big Game Initiative, launched by the USDA Natural Resources Conservation Service in 2022 in Wyoming, is a great example of how financial and technical assistance for landowners can improve their agricultural operations in ways that also conserve and improve habitat for migratory big game. The initiative has since expanded into Montana, Idaho, and Colorado.

By working together, we can ensure migratory herds roam the West’s range long into the future.

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