How bighorn sheep use crowdsourcing to find food on the hoof

If you’re a hungry human, you’re probably in luck: Crowdsourced apps like Yelp can help you find food in a pinch. But what if you’re a bighorn sheep? A new study shows how these grazers get food on the hoof—even as their “restaurants” shift from location to location.

Each spring, a green wave of plants rolls over the world’s temperate zones, as new growth pops up from south to north—and from lower to higher elevations. Biologists have long debated whether the following herds of grazers are born with these migration maps built into their brains or whether they have to learn the route from the rest of the herd.

To find out, scientists studied the seasonal movements of three groups of grazers: bighorn sheep that had been in the same location for centuries, sheep and moose that had been relocated to their current grazing grounds between 10 and 110 years earlier, and sheep that had just recently been moved to a new grazing location. The researchers outfitted them with GPS collars and followed their movements as they migrated, comparing them to the richness of the vegetation along their routes, as measured by satellite data.

They found that the first group excelled at following the green wave of new growth. Sheep and moose in the second group had varying levels of success. And animals in the third group didn’t migrate at all, but ate what they could where they were.

It was the movements of the second group that were the most telling: The longer the sheep or moose had been at these new locations, the better they became at following the green wave, the researchers report today in Science.

The researchers also found that other factors, such as crowding, habitat loss, or increased predation did not strongly affect the tendency to migrate, suggesting that knowledge alone, either learned from others or gained by experience, helped the sheep take advantage of new growth. That suggests culture plays a vital role in how grazers find food, and that once such knowledge is lost—unlike old Yelp reviews—it may take decades to resurface.