Evidence suggesting that desire-state attribution may govern food sharing in Eurasian jays

Abstract

State-attribution is the ability to ascribe to others an internal life like one's own and to understand that internal, psychological states such as desire, hope, belief, and knowledge underlie others' actions. Despite extensive research, comparative studies struggle to adequately integrate key factors of state-attribution that have been identified by evolutionary and developmental psychology as well as research on empathy. Here, we develop a behavioral paradigm to address these issues and investigate whether male Eurasian jays respond to the changing desire-state of their female partners when sharing food. We demonstrate that males feed their mates flexibly according to the female's current food preference. Critically, we show that the males need to see what the female has previously eaten to know what food she will currently want. Consequently, the males' sharing pattern was not simply a response to their mate's behavior indicating her preference as to what he should share, nor was it a response to the males' own desire-state. Our results raise the possibility that these birds may be capable of ascribing desire to their mates.

Fig. 1.

Outline of the experimental procedures. Birds underwent each experiment—(A) specific satiety, (B) food sharing, and (C) observational specific satiety—in the order in which they are listed. Condition refers to whether the female was visible to the male during the prefeeding phase. In the (A) specific satiety and (C) observational specific satiety experiments as well as in (B, i) the seen condition of the food-sharing experiment, males could watch the females being prefed; while in (B, ii) the unseen condition of the food-sharing experiment, they had no visual access to the females during prefeeding. The prefeeding and test columns depict the type of food (MD = maintenance diet, W = wax moth larvae, M = mealworm larvae) and quantity (when applicable) given to each bird, with durations of the phases given in italics.

Fig. 2.

Average difference in the proportion of W eaten in the specific satiety experiment between the prefed W and the prefed MD trials (white box) and between the prefed M and the prefed MD trials (gray box). Boxes show the median and upper and lower quartiles (75% and 25%) of the data; whiskers show the maximum and minimum values. For individual data, see Tables 1 and 2.

Fig. 3.

Average difference in the proportion of W shared in the (B, i) seen and (B, ii) unseen conditions of the food-sharing experiment and eaten by the males in the (A) specific satiety and (C) observational specific satiety experiments between the prefed W and the prefed MD trials (white boxes) and between the prefed M and the prefed MD trials (gray boxes). Boxes show the median and upper and lower quartiles (75% and 25%) of the data; whiskers show the maximum and minimum values. For individual data, see Table 1.