Experimenter expectancy bias does not explain Eurasian jays' (Garrulus glandarius) performance in a desire-state attribution task.

Male Eurasian jays have been found to adjust the type of food they share with their female partner after seeing her eat 1 type of food to satiety. One interpretation of this behavior is that the male encoded the female's decreased desire for the food she was sated on, and adjusted his behavior accordingly. However, in these studies, the male's actions were scored by experimenters who knew on which food the female was sated. Thus, it is possible that the experimenters' expectations (subconsciously) affected their behavior during tests that, in turn, inadvertently could have influenced the males' actions. Here, we repeated the original test with an experimenter who was blind to the food on which the female was sated. This procedure yielded the same results as the original studies: The male shared food with the female that was in line with her current desire. Thus, our results rule out the possibility that the Eurasian jay males' actions in the food sharing task could be explained by the effects of an experimenter expectancy bias. (PsycINFO Database Record