Hierarchies and Dominance Behaviors in European Pond Turtle (Emys orbicularis galloitalica) Hatchlings in a Controlled Environment

SIMPLE SUMMARY: Many animal societies are organized in hierarchical structures, which are determined by behavioral interactions among individuals. However, the study of complex social relationships in reptiles, particularly in turtles, is still poorly studied and usually performed on adult individuals. We investigated the establishment of hierarchical social structures in hatchlings of the European Pond Turtle during their first year of life. We reared three small groups of turtles in a controlled environment and observed their pairwise interactions during food supply, on a daily basis for seven months. Data analysis was aimed at identifying the eventual hierarchical structures and describing their characteristics. The hatchlings started interacting at two months old and all groups established stable hierarchies after about one month of interactions. Turtles interacted by head bites, tail bites and mounts, but the effectiveness of these behaviors in establishing the rank of individuals was low. Both the interactions’ outcome and social ranks were independent from the turtles’ size. This study is first proof of the emergence of a social structure in the hatchlings of the European Pond Turtle in captivity, a condition that is often faced in ex situ conservation projects for this protected species. ABSTRACT: Few species of reptiles are known to establish stable social structures and among these, chelonians provided scarce and conflicting results. Moreover, studies on turtles are usually performed on adult individuals. In this study, we checked whether and when hatchlings of the European Pond Turtle (Emys orbicularis galloitalica) established stable hierarchical structures in their first year of life, whether hierarchies were stable in time and how steady they were. We also verified whether social ranks were associated to the individuals’ size. We observed dyadic interactions daily within three small groups of turtles reared in a controlled environment for seven months. After two months, the hatchlings started to interact and progressively established stable hierarchical structures. However, the effectiveness of the three types of observed aggressive behaviors in reversing social ranks was low and the resulting hierarchies were flat. We did not find a significant effect of the turtles’ size on their interactions’ outcome and hierarchy structure. Our results provide clear evidence of the development and the characteristics of social behaviors in young reptiles in captivity. This study could be a starting point for investigating social structures in wild populations.