Hide some gold coins in your backyard, and you'll probably check around to make sure no one is spying on where you stash them. Eurasian jays are no different. A new study finds that the pinkish-gray birds with striking blue wing patches are not only aware that others may be watching while they stash their nuts and seeds for the winter, but also might be surreptitiously listening, too. In response, they change their behaviors—stashing nuts in quieter places, for example. The findings suggest that the jays may be able to understand another's point of view, an ability rarely seen in animals other than humans.
Several species of jays and crows, collectively called corvids, cache food to eat later. They also spy on one another and steal from each other's caches. The behaviors have led to what researchers term an evolutionary arms race, with the birds evolving various strategies to outwit their rivals, such as hiding nuts in the shade or behind barriers, or moving their cache to new locations. In the wild, Eurasian jays are often robbed by other species of birds such as Jackdaws and crows, as well as by their own mates. "They're also very good vocal mimics, imitating the calls of raptors and songbirds in the wild, and our voices in the lab. And that means that auditory information is a big part of their cognitive repertoire," says Rachael Shaw, a behavioral ecologist at the University of Cambridge in the United Kingdom, who led the new study while a graduate student in comparative psychologist Nicola Clayton's lab at Cambridge. But do the birds, which are also very secretive, understand that the scratching and rustling sounds they make while caching their nuts in the ground might draw the attention of another bird? Other researchers working with Clayton had previously shown that Western scrub jays from North America would avoid hiding nuts in noisy gravel if a rival was nearby and could hear them.
To find out if the Eurasian jays were equally sensitive to the noise they made while concealing their food, Shaw tested eight of the captive birds, providing them with 30 peanuts and two trays for caching. One tray contained soft sand, which was a quiet substrate; the other tray held gravel, a noisier substrate. In some tests, the caching jay worked while a competitor watched and listened. In others, the jay's rival was within earshot, but couldn't see what the other jay was doing.
Shaw and Clayton found that like the scrub jays, the Eurasian jays preferred the quiet sand for stashing their nuts, especially when another bird could hear them but even when they were alone. Four birds that used the gravel when a rival was watching and listening changed their behavior when the competitor could only eavesdrop but not see them, the two researchers report online today in the Proceedings of the Royal Society B. They then stored most of their nuts in the sand or other quiet locations away from the tray. "That suggests that the jays were using a specific cache-protection strategy. They were reducing the amount of noise they made," Shaw says, just as the scrub jays do. But, she adds that the Eurasian jays' overall preference for hiding nuts in the sand suggests that these birds, which are known for their secretive ways, may generally try to avoid drawing attention to themselves.
Shaw then added a new twist, testing birds that were looking to steal. Eurasian jays may hop about stealthily in the wild, but they are also noisy birds, known for their raucous calls. But in Shaw's experiment they fell as silent as church mice, when given the opportunity to watch another jay hide its food. "It shows that the pilferers are strategizing; they're aware that the other bird is listening, and if they're going to spy successfully, they need to be quiet," Shaw says.
"The flexibility of the jays' reactions in different social situations, and the use of these tactics across different sensory domains [sight and sound] supports the notion that the jays have something like a theory of mind—an understanding of others' points of view," says Lisa Leaver, a behavioral ecologist at the University of Exeter in the United Kingdom who was not involved in the study. "It's absolutely fascinating to see that the jays are so sensitive and can switch strategies depending on the context and on what others can see and hear," adds Alex Taylor, an evolutionary psychologist at the University of Auckland in New Zealand. "They're obviously treating different information in different ways."
The study adds to a growing list of animals, including dogs, chimpanzees, and monkeys, that are sensitive to what others can see and hear, notes Juliane Brauer, a comparative psychologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. But she points out that so far, only dogs and jays seem to pay attention to the noise they themselves make and that others can hear. "The question is do they really understand what others can hear and see." On that, the jury is still out.