Swipe right to match the stripes - pair compatibility in the okapi ex-situ programme: A look at male aggressive behaviour during breeding introductions

Zoo population management programmes can safeguard genetic diversity and ensure the survival of endangered species. The selection of mates for achieving genetic and demographic goals within the managed population means that free mate choice is very limited. This lack of choice may lead to pair incompatibility among the selected pairs, which have the potential to undermine the whole programme due to low reproductive outcomes. In the okapi Okapia johnstoni ex-situ programme in European zoos, cases of male aggression during breeding introductions have been attributed to a lack of compatibility among the pair. However, very little is understood about which factors are linked to the occurrence of this behaviour. In this study, a questionnaire was sent to zoos holding okapi, requesting information about the mating behaviour of their pairs and husbandry aspects. Subsequently, the occurrence of male aggression in the pairs was analysed against age difference, female oestrus management and socialisation of both individuals at a young age. Age difference and socialisation did not explain the occurrence of male aggression. Instead, the female oestrus management chosen for each pair was a significant factor predicting the occurrence of male aggression. Pairs that were allowed together regularly during the female’s anoestrus period displayed significantly fewer aggressive behaviour compared to those that were only given access during the female’s oestrus. We suggest that regular introductions might promote familiarity and the exchange of important reproductive cues among the pair, which leads to successful breeding introductions. However, based on our results, we cannot determine whether the two different oestrus husbandry approaches cause the occurrence of aggression or whether the occurrence of aggression influences which husbandry is applied to any given pair. We believe that the keeper’s perception of pair compatibility may be a confounding factor in our results since keepers are often hesitant to introduce animals outside of the female’s oestrus if they perceive the pair as incompatible or if aggression has occurred. Similar animal keeper biases have been documented in other breeding programmes, and further research is needed to better understand pair compatibility in okapi.