Mental state attribution is the ability to ascribe internal states such as beliefs and desires to others. Behavioural evidence for mental state attribution must satisfy a number of criteria. The behaviour cannot be the result of a response only toward observable cues such as changes to another individual’s behaviour. Instead the behaviour must be based on the attribution of an internal state. Moreover, the capacity to attribute mental states should not be limited to a single behaviour or context.

Here, we will present a series of experiments that test whether or not Eurasian jays meet the behavioural criteria for desire state attribution. These experiments build on previous work that has investigated the food sharing behaviour of Eurasian jays and their cache protection strategies. In previous food sharing studies male Eurasian jays altered the type of food they shared with their partner depending on what she had been sated on. Previous studies of Eurasian jays’ cache protection strategies have focused on whether the jays take into account how well an observer perceives a cache location but have not considered jays’ sensitivity to another’s desire.

In line with the criteria for mental state attribution we demonstrate that the male jay’s ability to share food that caters for their partner’s desire is highly flexible and is not triggered by a single eliciting cue. Furthermore, we investigated whether cache protection tactics employed by Eurasian jays are sensitive to the desires of an observer. In this competitive context we found that the jays would choose to cache less of the food type that an observer currently desires than of a food type the observer is currently sated on. Finally, we will discuss the implications these results have for considering whether Eurasian jays are capable of desire state attribution.