Discrimination of conspecific head orientations and learning set formation in Bengalese finches

Animals detect others’ gaze direction, such as predators, prey, and courtship mates, to enable adaptive behavior. However, head movements play a more significant role in gaze shifts in birds than eye movement because of the flat eye shape. Additionally, most birds with laterally placed eyes usually turn the lateral face to the target. Therefore, we used Bengalese finches to examine whether songbirds can discriminate between conspecific frontal and lateral faces and divide head orientations in different angles into two categories. In experiments, birds were trained by operant conditioning to discriminate stimuli consisting of conspecific frontal and lateral head images. Eight out of nine birds finished discrimination training and test sessions. The results indicate that Bengalese finches can discriminate gaze direction by the head orientations. Furthermore, as the number of stimuli set increased, fewer trials were needed to achieve the criteria, which suggests that birds have developed a learning set during the training. However, we did not find a clear discrimination boundary for head orientation categorization.