At first glance, the behavior of scrub jays seems like a sign of intelligence. Whenever they notice another bird looking at their food, they will hide their food as far away as possible...then start doing that over and over again.
This process, known as recaching, is meant to confuse any potential spies and protect the scrub jay's supply of worms. The final step - and the one most often pointed to as a sign of intelligence - is where the scrub jay reburies its worms one last time after it's clearly alone. Researchers had previously argued that this meant the scrub jay was capable of imagining itself in the position of another bird and realize it's still possible for another scrub jay to know where its food is. If it were capable of that sort of reasoning, it would possess a trait that is otherwise exclusive to primates.
But now researchers at the University of Gronigen in the Netherlands have a different, rather less flattering suggestion. Instead of invoking major cognitive abilities, they suggest the scrub jays keep hiding food simply because the chaos of recaching leaves them stressed, confused, and maybe a little paranoid, as they explain in PLoS ONE:
Inspired by experimental data, we assume that re-caching is not motivated by a deliberate effort to safeguard specific caches from theft, but by a general desire to cache more. This desire is brought on by stress, which is determined by the presence and dominance of onlookers, and by unsuccessful recovery attempts.
The researchers tested this idea by creating a computer simulation that would approximate how scrub jays act in the wild. Crucially, this simulation had no way of putting itself in the shoes of other virtual birds, which means if it kept hiding food after all onlookers were gone then the cognitive theory couldn't be the answer:
Our results show that the ‘virtual bird' acts as the real birds did; its re-caching reflects whether it has been watched, how dominant its onlooker was, and how close to that onlooker it has cached. This happens even though it cannot attribute mental states, and it has only a single behavioral rule assumed to be previously learned. Thus, our simulations indicate that corvid re-caching can be explained without sophisticated social cognition. Given our specific predictions, our theory can easily be tested empirically.