Every day we infer mental events from the behavior of others. We assume other people have minds and mental experiences that resemble our own and we use our understanding of mental processes to try to predict their behavior. This is known as having a theory of mind.
Human children develop a theory of mind through several regular stages at roughly predictable ages, from toddlerhood to about age five. Whether other species possess a theory of mind is contentious, and many consider the trait to be uniquely human. Experiments with great apes have yielded mixed results, open to different interpretations by scientists on either side of the question.
If we can't find definitive proof for a theory of mind in our closest relatives, then the claim that it exists in a common backyard bird might seem remarkable. But in a new study male Eurasian jays passed a test for a crucial component of theory of mind known as state attribution. It's the understanding that other individuals have their own desires and motivations. The male birds in the study responded to the changing appetites of their mates by bringing them different foods, demonstrating not just thoughtfulness but an understanding of another bird's mental state.
By Hans-Jörg Hellwig (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Nicola Clayton and colleagues at the University of Cambridge in England took advantage of the courtship habits of male jays, who win females' favor with gifts of food. The researchers first allowed male jays to watch as the females ate their fill of one of two foods: mealworm larvae or waxmoth larvae. They then let the males choose one of the two foods to offer the females as a gift.
Like people, jays prefer variety. The researchers hypothesized that if a male jay could attribute a desire to his mate and had just watched her devour one type of food, he would choose the other type of food as his gift. And that's exactly what happened. Male jays consistently chose to offer the food their mates hadn't been eating previously. Importantly, the researchers included an "unseen" condition in which the male couldn't see what the female had eaten to rule out the possibility that she was somehow indicating her preference with subtle social cues. When the eating females were hidden from sight, the males could not provide the opposite food choice later on.
By Jerzystrzelecki (Own work) [CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
Clayton and colleagues' experiment is elegant and well-controlled. They tested seven pairs of birds 20 times each, switching around the type of food the females were allowed to eat between trials. The males' gift choices were not simply responses to the females' behavior, as they needed to see what their mates had previously eaten to predict the food they would currently want. The researchers also ruled out the possibility that the males were choosing the type of food that they wanted. In very careful language, the authors conclude their results "raise the possibility that these birds may be capable of ascribing desire to their mates."
By Jakub Hałun (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
And while state attribution is just one component of a theory of mind, previous research out of Clayton's lab
suggests jays possess other components, as well. Clayton has shown that jays are able to plan for the future, even when they anticipate it will conflict with their current desires and motivations. Over several experiments, Clayton's group has also demonstrated jays differentiate between dominant and subordinate birds, and between their mates and other birds, and remember which individual watched them when they were hiding food. The jays appear to be aware of what others have seen and not seen, and which particular birds are a threat, and they will move their food to a more hidden location accordingly. These behaviors demonstrate another component of a theory of mind known as knowledge attribution
; jays know that different individuals may know different things.
Clayton is careful to not anthropomorphize her subjects, and has written that the birds' abilities may not necessarily require a "human-like" theory of mind. However, it is clear that they possess something special, perhaps an avian theory of mind, not exactly like our own but not entirely dissimilar. Her research inspires us to look for intelligence and abilities in all animals, not just the ones with fur and faces like our own.
Cheke, L.G. and Clayton, N.S. 2012. Eurasian jays (Garrulus glandarius) overcome their current desires to anticipate two distinct future needs and plan for them appropriately. Biol. Lett.8(2): 171-175. doi: 10.1098/rsbl.2011.0909
Clayton, N.S., Dally, J.M. and Emery, N.J. 2007. Social cognition by food-caching corvids. The western scrub-jay as a natural psychologist. Philos Trans R Soc Lond B Biol Sci. 362(1480): 507-522. doi:10.1098/rstb.2006.1992
Dally, J. M., Emery, N. J. and Clayton, N. S. 2006. Food-Caching Western Scrub-Jays Keep Track of Who Was Watching When. Science. 312(5780): 1662-1665. doi:10.1126/science.1126539
Ostojić, L., Shaw, R. C., Cheke, L. G. and Clayton, N. S. 2013. Evidence suggesting that desire-state attribution may govern food sharing in Eurasian jays. PNAS. 110(10): 4123-4128. doi:10.1073/pnas.1209926110
Thom, J. M. and Clayton, N. S. 2013. Re-caching by Western Scrub-Jays (Aphelocoma californica) Cannot Be Attributed to Stress. PLoS ONE 8(1): e52936. doi:10.1371/journal.pone.0052936