“The big highways, a lot of the herd is using. Once you identify those, that becomes an important target for conservation,” said Matthew Kauffman, USGS lead scientist for the mapping project.
Human development — homes, roads, fences, oil and gas fields and mining operations — increasingly interferes with Western migrations, sometimes with little awareness of what’s at stake for animals cherished by wildlife watchers and hunters alike.
Mule deer, for example, plummeted in number when home development surged in the Wyoming ski enclave of Jackson Hole decades ago, said Mike Eastman, a writer and wildlife photographer who grew up in the area and used to guide hunters there.
“Mule deer are real susceptible to a lot of people in an area, and it just kind of pinches them off,” Eastman said. “They’re kind of like steelhead or salmon and can’t get up there because a dam is in the way.”
Fences that impede mule deer — big-eared cousins of whitetail deer — or pronghorn antelope can be deadly. Roads, such as Interstate 80 from Wyoming to California, also hold up and kill migrating big game animals.
While some animals, such as migratory birds, can genetically inherit knowledge about when and where to migrate, others learn from their elders. Reintroduced populations of Western big game animals need decades to rediscover migration routes, research suggests.