Cognitive mechanisms of transitive reasoning in the adult domestic hen

Transitive inference (TI) is a reasoning ability that allows animals to indirectly connect two components, knowing their respective relationship to each other (if A>B and B>C then A>C). Few bird species have been tested for TI to date, which limits our knowledge of the phylogenetic spread of such reasoning ability. Here, we tested TI in adult laying hens. Five hens had to learn direct relationships in a non-perceptual sequence of six items, varying in color and shape (A>B>C>D>E>F). The birds were trained to always peck at the priority item among two adjacent ones. Then, 12 testing sessions were implemented, comprising 3 unrewarded inference trials each, with one of each possibility per session (B-D, B-E, and C-E). All subjects showed TI within 12 inference trials. Further testing revealed that the hens were able to respond transitively using the respective colors of the items as the only cue, but not their shape. Our analysis showed that their performance was likely dependent on the residual value of the extreme items (A, F) over the others. Finally, we showed the absence of other possible response strategies through the configuration of the sessions. These results contribute to a better understanding of transitive reasoning in birds.