Do birds (pigeons and bantams) know how confident they are of their perceptual decisions?

Rhesus monkeys are known to recognize confidence about their immediate perceptual and cognitive decisions by using a betting procedure (Son and Kornell in The missing link in cognition: origins of self-reflective consciousness. Oxford University Press, New York, pp 296-320, 2005; Kornell et al. in Psychol Sci 18:64-71, 2007). In this report, we examined whether this ability is shared in two avian species (pigeons and bantams) in order to know how widespread this metacognitive ability is among animals. We trained pigeons and bantams to search for a differently colored disk (target) among others (distracters) displayed on a touch-sensitive monitor. In test, the subjects were required to choose one of two confidence icons, "risk" and "safe", after the visual search. A peck at the "risk" icon after a correct response in the visual search (i.e., a peck at the target) was reinforced by food and light, while that after an incorrect response (i.e., a peck at a distracter) resulted in a timeout. A peck at the "safe" icon was always reinforced by food and light, or by light only, regardless of the visual search result. The percentages of "safe" choices after incorrect responses were higher than after correct responses in all six pigeons and two of three bantams. This behavior generalized to novel stimuli in some subjects, and even to a novel line-classification task in a pigeon. These results suggest that these two distantly related avian species have in common a metacognitive ability that allows them to recognize confidence about their immediate perceptual decisions.