Sheep Teach Each Other How to Migrate Long Distances

Bighorn sheep migrate on long journeys, following a wave of green as plants come to life. Instinct doesn't teach this, but culture does.

Bighorn sheep, like this ram photographed in Montana's Yellowstone National Park, must learn the best migration strategy from their mothers.

Large migrations are some of nature's greatest spectacles. Wildebeest and zebra chase the rains through the Mara ecosystem every year, monarch butterflies trace a path from Mexico to Canada and back, and tiny songbirds fly nonstop for days at a time. And now scientists are starting to figure out how they know where to go, and when.

Some of these animals, they’ve found, have their migration pathways written into their genes. A songbird hatched in a laboratory, having seen nothing of the natural world, still attempts to begin migration at the right time of year and in the right cardinal direction.

But large mammals like bighorn sheep and moose are a different story. Wildlife researchers have long suspected that they require experience to migrate effectively, that their annual journeys are the result of learning from one another, not of genetic inheritance. A new study, published Thursday in the journal Science, suggests that those hunches may be correct—some animals must learn how to migrate.

The existence of collective information and knowledge, that can be passed from older animals to younger ones, is a form of “culture,” researchers explain. And when animals learn as a result of social interaction and the transfer of this information, that’s a type of cultural exchange—as opposed to genetic.

On the mountains and plains of North America, massive herds of ungulates—hoofed creatures, like caribou, elk, moose, and bighorn sheep—migrate from high altitude breeding grounds to warmer, lower altitudes during the harsh winter, following the growth of new greenery. Ecologists call this “surfing the green wave,” and the new study finds that bighorn sheep and moose have to learn how to surf.

Wyoming’s Incredible Animal Migrations Revealed as Never Before

Mother Knows Best

Due to market hunting and disease transmission from domestic sheep, bighorn sheep populations began to plummet in the late 1800s. Starting in the early 1970s, wildlife officials and hunting groups began to re-establish wild sheep populations by moving individuals from surviving herds into areas that were once part of the species’ historical range.

The history of these translocations, combined with newly available GPS tracking technology, allowed University of Wyoming ecologist Matthew Kauffman and his team to trace the development of migration behaviors. Led by graduate student Brett Jesmer, the team affixed GPS collars to 129 bighorn sheep from established populations at least two hundred years old, along with 80 sheep and 189 moose that had recently been moved.

“With ungulates, the thought was that there is no genetic program. Instead they just have to learn how to do this,” says Kauffman. And if that’s the case, he says, the animals that have been moved shouldn’t migrate, because they wouldn’t yet have learned a new migration route.

That's exactly what they found.

The upper eyelids and snout of the Malaysian horned leaf frog protrude sharply from its head, creating the illusion of horns.

Male Nubian ibex ram one another with their long curved horns during battles for dominance. These majestic desert-dwelling goats also use their horns to intimidate potential predators.

The aptly named rhinoceros ratsnake sports a rhino-like protrusion on the end of its snout. Herpetologists aren't sure what purpose the horn serves, but the scaled ornamentation certainly sets this snake apart from others on the rain forest floor.

The spectacular spiraled horns sported by the South African oryx make them a target for trophy hunters. Females use their horns to fight off predators, while males use them to keep other males out of their territory.

The horned guan does not have a true horn, nor is it a true guan. Its "horn" is merely a flap of brightly colored skin that helps it stand out amongst the colorful cloud forest foliage. This member of the Cracid family inhabits South and Central America, and spends most of its time in trees, feeding on fruit and leaves.

The corkscrew-like horns of the bukharan markhor are coveted by trophy hunters, which is why the species is endangered throughout its range in South and Central Asia. Male bukharan horns can reach 63 inches (1.6 meters) in length, and some cultures believe they have medicinal properties.

The four pointy horns that protrude from the snout of the four-horned chameleon add to the animal's already dragon-like appearance. These resilient reptiles can sport six or more horns at any given time. However, these horns are fragile and can easily be broken off.

Both male and female sable antelope posses a pair of ringed horns that arch elegantly toward their backs. Males sport slightly longer horns than females, which can reach 65 inches (1.6 meters) in length. When two of these African mammals go head to head, they drop to their knees and butt horns.

This male mountain goat shows off its stubby set of black horns. These high-altitude animals live atop North America's tallest mountains. Males and females are equipped with beards and horns, and both use them well. Both sexes intimidate their rivals by bowing their heads to show off their surprisingly sharp horns.

The Texas horned lizard is well-equipped to defend itself against predators. In addition to a set of sharp horns, which are an extension of its skull, this lizard is covered in spikes that protrude outward when it feels threatened. The American reptile can also squirt a foul-tasting liquid from the corners of its eyes.

Pronghorn antelope have a unique set of branched "horns" that can grow up to a foot long. These "horns" are neither true horns nor antlers, but bony extensions of their cranium. Male pronghorns use these pointy protrusions during bouts with rival males.

Two scimitar-horned oryxes showing off their long, sharp-tipped horns. All scimitar-horned oryx have a set of impressive ribbed horns that can extend several feet. These desert-adapted antelopes roam Africa's dryest regions, where they sometimes do not drink for months at a time.

The eastern black rhino is adorned with an elegant set of hefty horns. Poachers will risk life and limb to get their hands on rhino horn, and as a result, the eastern black rhino is critically endangered. Rhino horn is used in traditional Chinese medicines, but there is no evidence to support the idea that the material has any medicinal value.

The hickory horned devil caterpillar is the larval stage of the regal moth, which is among the largest moths in North America. Despite this prickly caterpillar's menacing appearance, it is completely harmless. These caterpillars molt four times before they metamorphize. The final molt produces a caterpillar with tubular, black-tipped horn-like appendages.

The "horns" of the horned frog are extensions of the amphibians' brow. These devilish creatures have a famously strong bite and sticky tongue, which they use to take down insects and rodents.

The dall, or thin horn sheep, can be found roaming the subarctic mountain ranges that stretch from Alaska to Canada. Males use their thick, yellow-tinted horns to ward off rivals, and on occasion, to knock predators over the edges of cliffs.

Most, but not all horned desert vipers have "horns." These venomous, desert-dwelling vipers can be found slithering through sandy deserts in Africa and the Middle East.

An Eastern giant eland shows off its arresting coloration and tightly spiraled horns. The "giant" in its name refers to its massive horns, which can reach four feet (1.2 meters) in length in males. These elegant antelopes are becoming more scarce in their native African range as a result of excessive hunting and habitat loss.

The metallic color and disproportionately large horns make male rainbow scarabs easy to identify. These horns are used in fights with rivals and may also play a role in attracting a mate. Rainbow scarabs are the better-looking cousins of the North American dung beetle and a favorite among insect collectors.

The addax is a critically endangered species of antelope found only in the Sahara desert and parts of Morocco. Between their long twisted horns, which can reach close to three feet in length, is a tuft of dark hair. Sometimes called screwhorn antelope, addaxes are slow-moving and docile, which makes them an easy target for trophy hunters.

Male Atlas beetles have three smooth, slender horns on their head and thorax that they use in fights with other males. These Southeast Asian natives are named after the Greek god Atlas, who was condemned to hold up the sky for eternity.

A blackbuck from the Ellen Trout Zoo leans close to the camera. The long, ringed horns of the blackbuck, or Indian antelope, can reach nearly three feet (about a meter) in length. All males and some females have horns. Males push one another with their horns during battles for dominance.

Tap images for captions

“With bighorn sheep and moose, and this is true for deer and elk as well, the young are highly dependent on their mothers. For pretty much the first year of life, they're basically following mom around,” says Kauffman. “So they're developing this spatial memory of the migration route from mom.”

And of the 80 translocated sheep, only seven even attempted a migration, and these were individuals that were integrated into pre-existing herds of several hundred migrating sheep. That suggests that migration knowledge can be transferred horizontally, among adults, not just vertically, through generations.

This isn't to say that ungulates couldn't have some innate motivation to seek out new opportunities. The issue is knowing how to do so while staying safe. “Knowing how to get from A to B usually involves crossing some habitats where there is a higher risk of predation, where maybe forage conditions aren't very good, so animals need to know where to go,” says University of Sherbrooke biologist Marco Festa-Bianchet, who was not a part of the study. "That's the part that needs to be learned."

Bighorn sheep can form groups, which facilitate the transfer of cultural knowledge. This group was photographed scaling a mountain in Yellowstone National Park.

Learning to Surf

An optimal migration would precisely line up with the peak of the green wave, with animals moving into new areas as soon as vegetation starts growing, while also avoiding risky areas full of predators. The new study shows that sheep and moose do learn to optimize new routes over time; the longer a population survives in a new habitat, the more effectively its members can surf.

Those animals who chance upon a more efficient migration strategy survive longer and leave behind more offspring. Those young learn how to migrate from their mothers, and acquire new knowledge along the way to even further refine their migration strategies. Taken together, this means that ungulate migration is a form of cumulative culture—says Kauffman, a system of behaviors passed from generation to generation, each cohort building upon the knowledge of their predecessors.

Moose, like this male photographed in Alaska's Denali National Park, lead more solitary lifestyles, which means it takes longer for knowledge to propogate through a population.

There's just one catch: for a newly translocated herd of bighorn sheep, it could take 50 or 60 years before half the herd becomes proficient at surfing the green wave. For moose, perhaps because they are more solitary creatures with fewer opportunities for social learning, it could take a century, or longer.

“Wildlife reintroductions, for all sorts of different species, often fail. This gives us a lens into why they fail,” says Kauffman. “They fail, in part, because animals don't have knowledge about how to exploit new landscapes.”

So when a road, a fence, or a new housing development disrupts an established mammal migration pathway, there are consequences not just for the herd's survival, but for its collective knowledge. And if mitigation strategies, like wildlife-friendly fences and highway overpasses and underpasses, aren't implemented quickly enough, it could take decades or even a century before a population can recover.  


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