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In the 1800s, there were so many bighorn sheep in Wyoming that when one trapper passed through Jackson Hole, he described “over a thousand sheep in the cliffs above our campsite.”
In the 1940s, the Wyoming Game and Fish Department began trying to move bighorns back into their historic habitats. Those relocations continue today, and they’ve been increasingly successful at restoring the extirpated herds. But the lost animals aren’t just lost bodies. Their knowledge also died with them—and that is not easily replaced.
Bighorn sheep, for example, migrate. They’ll climb for dozens of miles over mountainous terrain in the spring, “surfing” the green waves of newly emerged plants.
“The translocated animals were literally let out of a livestock trailer and started looking around at their new environment,” says Matthew Kauffman from the University of Wyoming. “And they almost entirely failed to migrate.”
Kauffman knows this because the translocated sheep were often fitted with radio collars, allowing him and his colleagues to compare their movements to those of bighorns that lived in the same place for centuries.
The team also used satellite images to measure how closely the sheep were tracking the waves of emerging greenery. Then, they compared the animals’ performance to two kinds of simulated sheep—naive ones that moved around at random, and omniscient ones that had perfect knowledge of the local plants.
“This changes how we think about wildlife habitats,” Kauffman adds.
Scientists have long wondered how migrating animals know where to go. In some cases, that knowledge is innate. Sea-turtle hatchlings read the Earth’s magnetic field to head off in specific directions, while hybrid songbirds will travel along routes that are halfway between those of their parents.
Ecologists have long speculated that ungulates—hooved animals such as deer, bison, and sheep—also learn to migrate, since many species seem to adopt the movement patterns of their mothers and peers.
To an extent, ungulates can find emerging greenery through local smells and sights. “But they also possess excellent spatial memory,” Jesmer says. “They can remember when a path greened up and time their movements to go to that area the next spring.”
That knowledge takes time to accrue, which the team showed by studying both the bighorns and five groups of translocated moose. The more time these animals spent in a new place, the better their surfing ability was, and the more likely they were to migrate.
Jesmer thinks this process likely occurs over generations: Individuals learn to move through the world by following their mothers, and then augment that inherited know-how with their own experiences.
That knowledge allows the animals to find plants early, when they’re young, tender, and more easily digested. And by eating high-quality plants, they can more easily pack on the fat and protein that gets them through harsh winters. “When they lose that knowledge, their populations will suffer,” Jesmer says.
Wildlife conservation isn’t just about raising the numbers on a population count.
Cultural losses are harder to see than disappearing habitats or declining populations, but they’re no less important, says Isabelle-Anne Bisson from the Smithsonian Conservation Biology Institute. “It’s another angle that’s crucial to document, in the face of unprecedented landscape and climate changes,” she said.
Humans have increasingly parceled the landscape into smaller and smaller chunks. We lay roads, erect fences, and build towns—all of which restrict the movements of wild animals and make migration more challenging.
Recognizing these problems, conservationists have increasingly tried to modify fences, create overpasses, and minimize development along so-called migration corridors.