Have you ever gone to get your horse from his paddock, only to have him “hide” his head behind a tree or a run-in … with his entire body remaining in plain sight? It might be obvious to us that the proportions don’t match up, but your horse might be “surprised” when he loses the game of hide-and-seek.

Swiss and German researchers say their latest study results indicate that horses don’t seem to be able to reason about size the way we do. In other words, it might not occur to horses that their 1,200-pound frames can’t quite hide behind a 5-inch-wide tree trunk.

“Our tests really show that horses fail to intuitively reason about object properties like solidity and weight,” said Federica Amici, PhD, of the University of Berne, in Switzerland. “But this doesn’t mean they aren’t intelligent. This simply means that horses may not especially require this ability.”

In their study, Amici and her fellow researchers tested 16 horses’ abilities to find a human hiding with a bucket of feed behind one of two black screens. In one test, the screens were of two sizes: one tall enough for a human to stand behind, the other not. In the second test, they tilted two equally sized screens toward the ground at different angles. A person could easily hide behind the bigger angle (80°) but not the smaller one (10°). The researchers had previously warmed the horses up to the idea that people can hide behind screens. They compared their results to control testing (two identically sized screens for the first test, two identically angled screens in the second).

They found that the horses didn’t perform better than they did with the controls in finding the human behind the different screen heights, Amici said. Essentially, the horses seemed to choose a screen at random.

They did slightly better than the controls with the different angles, she said. The difference wasn’t scientifically significant, but it indicated a trend suggesting the horses might have reasoned slightly more that a human probably wouldn’t hide with a bucket under a 10° angle.

“Our findings have practical implications, because they tell us a lot about how different species see the world—what can be interesting for them, what can be surprising, which expectations they have, what they understand,” Amici said. “Knowing how they see objects around them, for instance, can be interesting for people to prepare enrichment devices or to more efficiently train them.”

Their study also leads to a better scientific understanding about animal cognition in general, she said. For example, it can give useful insight into how cognitive skills are distributed across species, which evolutionary factors explain this distribution, how domestication might play a role in it, what kinds of knowledge might be innate, and what kinds might be acquired through experience.

“Animals, like humans, face strong selective pressures not only to evolve specific body characteristics but also specific cognitive skills,” Amici said. “In other words, animals are perfect (or almost perfect) adaptations to their environment. Failing to find evidence of a cognitive skill should never be disappointing, but enlightening for us, as we can better understand how cognitive skills are distributed and why.”

With horses, it’s possible that “the benefits of reasoning about object properties like solidity and weight are simply trivial” to them, she said.

“We should not expect horses to ‘think’ like humans,” Amici said. “Horses are very sensitive and intelligent animals, but their intelligence is different from ours, because it has evolved as a response to the specific socioecological challenges horses faced during evolution. Understanding how they differ from us, and what they may have in common with us, is extremely interesting, but it is essential that we first understand that they are (like any other species) an ‘evolutionary product’ which is not better nor worse than any other one. It’s just the best one for the specific challenges faced.”

These results are preliminary. A test of 16 horses can’t give definitive conclusions about their cognitive abilities, Amici said. It’s also possible that the horses might have thought a human would be crouching behind the lower screen, she added.

“As one of the greatest researchers in animal cognition, Wolfgang Köhler (PhD, director of the Psychological Institute of the University of Berlin) once said, ‘Besides the creature being investigated, every intelligence test necessarily tests the tester,’ ” Amici said. “So before concluding that animals cannot do something, more tests are always needed.”

The study, “Domestic horses (Equus ferus caballus) fail to intuitively reason about object properties like solidity and weight,” was published in Animal Cognition.