How Does Castration Change Integration of Immature Males in Their Familial Group Network in Captive Western Lowland Gorillas?
Résumé
The European captive population of western lowland gorillas has successful breeding results and a healthy population development. With a harem social lifestyle and a balanced sex ratio at birth, management of the overpopulation of males begins to be problematic. For almost 20 years, bachelor groups have been established in zoos in order to counterbalance this trend but this solution is nuanced over time because of the recurrent agonistic conflicts recorded. This is why the European Endangered Species Program (EEP) considers castration as an alternative to manage the longevity and welfare of the captive population. This proposal has been made assuming that the mature castrated males may remain in their native family group in the presence of the silverback male without risking conflicts over access to females. Ten immature males have been castrated in 6 different institutions following the recommendation of the EEP committee. We collected all affiliative behaviours performed in proximity to one congener for 75 individuals of all age and sex classes living in 7 captive breeding groups (375 h of focal animal sampling, 5 h per individual). Among them, the results of 10 castrated immature males are compared to 10 “intact” immature males (five juveniles and five subadults in both categories compared). The analysis and visualisation of the different social networks provide precious knowledge of the social integration of immature ‘intact’ males in captivity. Moreover by comparing activity budgets and personality using the Gorilla Behaviour Index (GBI), “social preference” (contact or 1 metre proximity, instantaneous sampling) and “tolerance” (1 to 5 metres proximity), this study showed that castration has an impact on the socialization process of immature male gorillas, which are more cohesive in their group during maturation. This study also helps us to understand whether castration could be an acceptable tool to regulate the male overpopulation in captivity.