Abstract
Dispersal is widespread among the animal kingdom, and is associated with costs and benefits. For group-living animals dispersal often entails additional social costs of entering a new group. These costs may be especially apparent in primate species living in multi-male multi-female groups with male biased dispersal. Within these species, males
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face the challenge to obtain a new social position in a group with a cohesive core of related females, and multiple males to compete with. Up to now, researchers mainly focused on male-male competition during male group entry. However, the behavioural process accompanying integration (i.e. establishing a social position in a new group) is understudied. There is basic understanding of the behaviour of new males during group entry, but the role of resident females during male group entry has not received much attention. However, females are likely to interact with new males, based on female mate choice and the fact that new males may commit infanticide. Female tolerance may even be crucial for successful integration of new males. However, systematic studies on female behaviour during male group entry are lacking. This information is, however, critical to fully understand the social costs of male dispersal. The research described in this thesis aimed to gain better understanding of female-new male interactions during male group entry, through studying male introductions in captive naturalistic groups of rhesus macaques (Macaca mulatta) and long-tailed macaques (M. fascicularis). Interactions between resident females and new males were studied from an applied (Chapter 3-5) and fundamental (Chapter 2 and 6-8) point of view.
The applied studies focussed on improving the behavioural management strategies of captive primate groups and thereby enhancing animal welfare. The studies elaborate on the effect of management and introduction procedures on introduction success, and the development of quantitative measures to determine how introductions progress and whether they may succeed. The studies show that mimicking nature closely in management procedures and during introductions increases introduction success and the long-term stability of a male’s position in the group.
The fundamental studies focussed on quantifying all possible female-new male interactions, determining the fitness consequences of these interaction, and identifying which females interact with new males and why. The research showed that females can use aggression, affiliation and mating to affect the costs and benefits of male group entry, through the formation of bonds, limiting or stimulating mating access and the initiation of conflicts. Females can even prevent new males from entering a group. Factors such as infanticide risk, female reproductive state, the female’s social network and male condition may determine a female’s response to a new male. Overall, it is clear that females are active contributors to, and not passive onlookers in, the process of male group entry.
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