How individual, social, and ecological conditions influence dispersal decisions in male vervet monkeys

Abstract

Dispersal between social groups reduces the risk of inbreeding and can improve individuals' reproductive opportunities. However, this movement has costs, such as increased risk of predation and starvation, loss of allies and kin support, and increased aggression associated with entering the new group. Dispersal strategies, such as the timing of movement and decisions on whether to transfer alone or in parallel with a peer, involve different costs and benefits. We used demographic, behavioral, hormonal, and ecological data to examine the causes and consequences of 36 dispersal events from 29 male vervet monkeys (Chlorocebus pygerythrus) at Lake Nabugabo, Uganda. Adult males' secondary dispersal coincided with the conception season in females, and males improved their potential access to females by moving to groups with higher female-to-male sex ratios and/or by increasing their dominance rank. Males that dispersed with a peer had lower fecal glucocorticoid and androgen metabolite levels than lone dispersers. Subadult males were not more likely to engage in parallel dispersals compared to adult males. Dispersal was also used as a mechanism to avoid inbreeding, but changes in hormone levels did not seem to be a trigger of dispersal in our population. Our findings illustrate the complex individual strategies used during dispersal, how many factors can influence movement decisions, as well as the value of dominance and hormone analyses for understanding these strategies.

Role of immigrant males and muzzle contacts in the uptake of a novel food by wild vervet monkeys

“…In another population, long-term resident males also showed reduced responses to novel foods compared to other age-sex classes ( Nord, 2021 ). We suggest rather that the unique individual, social, and environmental factors that prompt a male to disperse ( L’Allier, 2020 ) may trigger a transitory exploratory behavioral syndrome ( Sih et al, 2012 ) that may subside again once males acquire more secure residency in a group. Since dispersal inherently involves heightened risk, periods of long-term residency would be well-served by a state characterized by reduced exploration and increased neophobia to balance the costs of risk-taking over the lifetime.…”

Role of immigrant males and muzzle contacts in the uptake of a novel food by wild vervet monkeys

“…In another population, long-term resident males also showed reduced responses to novel foods compared to other age-sex classes [50]. We suggest rather that the unique individual, social and environmental factors that prompt a male to disperse [51] may trigger a transitory exploratory behavioural syndrome [13] that may subside again once males acquire more secure residency in a group. Since dispersal inherently involves heightened risk, periods of long-term residency would be well-served by a state characterised by reduced exploration and increased neophobia to balance costs of risk-taking over the lifetime.…”

Variation of social strategies between bluff and unobtrusive immigrant males during integration into a new social group: a case study in Macaca thibetana

“…The causes of dispersal and the determination of successful dispersal are multifactorial (Greenwood, 1980;Alberts and Altmann, 1995b;Xia et al, 2019;L'Allier et al, 2022), whereas immigration is a critical and stressful process to be a long-term residency in a new social group (Marty et al, 2017b). Upon arrival in a new target social group, immigrant males faced elevations in aggression from intrasexual conspecifics of a new group (Ydenberg et al, 1988;Teichroeb et al, 2011).…”