Proximate factors influencing dispersal decisions in male mountain gorillas, Gorilla beringei beringei
Section snippets
Study Site and Subjects
This study was conducted in the Parc National des Volcans, Rwanda. Research groups of mountain gorillas have been monitored at this site since 1967 (for description of study site and groups, see: Fossey, 1983, Watts, 1984, Robbins, 1995, Bradley et al., 2005, Robbins et al., in press). Data come from 8 of 14 groups that have been studied by the Dian Fossey Gorilla Fund International (DFGFI); the other six groups did not have males of known ages that reached dispersal age. Group composition
Characteristics of Dispersal
Of the 31 males in the study that had reached the minimum dispersal age of 13.3, 14 (45%) dispersed and 16 (52%) remained in the group in which they became a silverback (one male died and thus his dispersal status was considered unknown) (Table 1). Dispersal ages ranged from 13.3 to 21 years (mean = 15.3; median = 15.6). Nondominant, nondispersing males ranged in age from 13.5 to 21.8 years (mean = 16.8; median = 16.7). This includes the male that died at 21.1 years of age but excludes an individual
Discussion
Natal dispersal is a common, although not ubiquitous, practise in male gorillas, seen in roughly 50% of the individuals in the current study. The average age of dispersal corresponded with age of physical maturity (estimated at 15–16 years; Watts & Pusey 1993), although males begin copulating and can sire offspring before dispersal age is reached (Watts, 1991, Robbins, 1995, Bradley et al., 2005, Stoinski et al., in press). For roughly two-thirds of males, dispersal was a single event: males
Acknowledgments
We thank the l'Office Rwandais du Tourisme et des Parcs Nationaux for permission to work at the Karisoke Research Center. Special thanks to the entire Karisoke staff for their observations and protection of the gorillas and to the many researchers and staff that contributed to the demographic database (see Gerald Steklis & Steklis 2007). F. Barabwiriza, J.D. ‘Fundi’ Hategekimana, E. Hitayezu, F. Ndungutse, F. Ngaruyintwali, J. Ngirila, T. Nsengiyumva, A. Sebatware, F. Uwimana, P. Uwingeli and
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2022, Hormones and BehaviorCitation Excerpt :Dispersal timing is also associated with the start of copulative behavior in female horses (Equus caballus: Monard et al., 1996), as well as puberty-related hormonal changes in female tammar wallabies (Macropus eugenii: Williams et al., 1998), owl monkeys (Atous azarae: Corley et al., 2017), and woolly monkeys (Lagothrix lagotricha: Abondano et al., 2021). Examples of pre-dispersal pubertal changes are also present in male mountain gorillas (Gorilla beringei: Stoinski et al., 2009), lions (Pantera leo: Pusey and Packer, 1987b), spotted hyenas (Crocuta crocuta: Holekamp and Smale, 1998), and yellow baboons (Papio cynocephalus: Onyango et al., 2013). However, dispersal typically occurs before puberty in some primates, including female northern muriquis (Brachyteles hypoxanthus: Strier and Ziegler, 2000) and male white-faced capuchins (Cebus capucinus: Jack et al., 2014).
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