Across Wyoming and the West, tens of thousands of big game animals are beginning their annual migrations from summer to winter range. They’ll be pushed down from mountains by snow and cold. They’ll follow whatever bits of food are still available before icy winter hits. Then in the spring, they will go back, following a green wave of vegetation.
It seems like a logical journey, an instinctual progression that each animal would simply know to accomplish. Many bird and insect species do the same thing, moving north to south, then south to north, dictated by internal genetics.
But for big game, that logic is wrong. Their urge to migrate, to follow the best food and escape the worst weather, isn’t genetic. It’s learned.
University of Wyoming researcher Brett Jesmer recently proved that hooved animals, such as bighorn sheep and moose, must learn from their families when and where to go. His groundbreaking study was published Friday in the journal Science.
The paper, “Is ungulate migration culturally transmitted? Evidence of social learning from translocated animals,” details years of research and more than a decade of data collected by wildlife managers in Wyoming and Idaho. It ultimately concludes that big game do not inherently know to migrate.
“The take home message is to keep migrations intact,” said Doug McWhirter, the Wyoming Game and Fish Department’s Jackson wildlife management coordinator. “It can be very difficult to recreate them if not impossible, so don’t mess them up in the first place.”
Jesmer started working on the project with the theory that big game – or ungulates, as they’re called – learn where to migrate from others in their groups. But that had always just been a theory.
He decided a few years ago to dive into millions of data points collected from state agencies and UW and housed at the Wyoming Migration Initiative to see if his theory proved true.
“Ecologists assumed ungulate migrations were learned, passed from mother to offspring based on relatively simple observations but we lacked the data to test this conclusively until recently, and so that is what inspired us to do this study,” he said.
The data came in the form of way points collected from countless tracking collars that have been used since the early 2000s. The study was largely possible because of the large number of bighorn sheep relocations across the state in the last 50 to 70 years.
Bighorn sheep were extirpated – which essentially means locally extinct – beginning in the mid-1800s and into the early 1900s. They were slaughtered for food with the development of the West and died from disease brought largely by domestic sheep, Jesmer said.
Beginning in the 1950s, wildlife agencies and conservation groups began translocating wild sheep back into their historic range.
“The idea was, if it was innate migration, when we translocated sheep from the Wind River Range to the Wyoming Range, they would have started to migrate rather quickly,” Jesmer said. Small migratory songbirds, for example, will attempt to migrate if they are moved to a new location.
“If the sheep didn’t migrate, it might indicate that it would take learning and longer periods of time,” he added.
And that’s just what they found.
Sheep translocated in the ‘60s were just now beginning to track what ecologists call the “green wave” or the green up of food in the spring, he said. Wild sheep that were translocated into an existing migratory herd, however, more quickly learn how to migrate.
“Information is passed from mother to young, and then the young knows how to find patches of forage in the spring. Throughout that animal’s experiences it is also learning to improve upon what is passed from its mother, and then it passes it on,” he said. “This knowledge accumulates overtime, and they increasingly learn how to optimally use the landscape.”
While the data and paper are complicated, the final message is not: Don’t lose migrations.
States like Wyoming are uniquely positioned to maintain their long migration routes. It currently houses massive elk migrations in and out of Yellowstone National Park as well as the longest known pronghorn and mule deer migrations. Much of the state’s landscape is still intact.
But those migration routes can be broken, interrupted by energy development, subdivisions, roads and fences, Jesmer said.
Why does it matter?
Because the ability to migrate is what maintains large, robust herds. Wildlife adapted to follow the best food and escape the worst weather. Without that knowledge, their numbers could suffer, said McWhirter.
"This study clearly indicates that the best way to conserve migration corridors is to protect the landscapes that these corridors depend on today,” said Matt Kauffman, one of Jesmer's doctoral advisers and a wildlife researcher with the U.S. Geological Survey's Wyoming Cooperative Fish and Wildlife Research Unit at UW. “Which will also maintain the cultural knowledge that helps sustain abundant herds."
Could humans help big game to more quickly learn migration routes? It sounds far-fetched, but is possible, said Jesmer.
A famous whooping crane project put human pilots in ultralight gliders to escort cranes from Wisconsin to their winter grounds in Florida. The study was also published in Science.
That kind of guidance hasn’t been done with big game before, he said, but it could work. Jesmer then added that ultimately, it would be easier to simply prevent the routes from being lost.