要旨
Living in large, stable groups is often considered to favour the evolution of cognitive abilities related to social living, such as the ability to track relationships among group members and to make transitive inferences about relationships based on indirect evidence. Greylag geese are relatively small brained, but live in complex societies with social support and clan structures. They form dominance hierarchies in which families dominate pairs and unpaired individuals. However, competition is costly and the ability to transitively infer relationships among flock members may be highly advantageous. We tested five free-living, juvenile greylag geese embedded in a flock of 150 birds for their ability to track multiple dyadic relationships and their transitive inference competence. Individuals were trained on discriminations between successive pairs of five implicitly ordered colours (A–E). All individuals learned to track four dyadic relationships simultaneously and showed transitive inference when presented with nonadjacent colours. Remarkably, the amount of training required was related to the individual’s early social environment. Our study is one of the first to show transitive inference in a precocial bird and suggests an influence of early social experience on sociocognitive abilities. Furthermore, it improves our understanding of social complexity as an important selection pressure for the evolution of cognition.
