Social and reproductive strategies of male mantled howlers (Alouatta palliata) at La Pacifica, Costa Rica

This dissertation examines the competitive and cooperative strategies of male mantled howlers (Alouatta palliata) living within a fragmented habitat at La Pacifica (LP), Costa Rica. Mantled howlers exhibit considerable intraspecific variation in their social behavior, and there remains much to learn regarding the nature of their sociality and the proximate mechanisms that underlie it, particularly among males living in multimale groups. In contrast to males at other mantled howler study sites, males at LP had higher rates of within-group agonism, and exhibited clear dominance hierarchies. Both groups inhabited a fragmented forest, which may exert greater pressure to compete for both food and reproductive resources than mantled howler males living in more intact forests. However, data from this dissertation also suggest that males may adjust competitive relationships as forest fragment characteristics within the same population vary. The group inhabiting the larger forest fragment experienced higher intergroup competition but lower intragroup competition than the group inhabiting the smaller fragment, allowing higher-ranking males to be more tolerant of subordinates accessing key resources, including females, in order to cooperate in group defense. Despite clear hierarchies, males at LP nevertheless form both preferred and avoided associations with specific males, which suggest that cooperative relationships among males have adaptive value. Neither rank nor age emerged as clear drivers shaping competitive and cooperative relationships. Collectively, these results suggest that male mantled howlers show considerable flexibility in their social relationships that are likely dependent on a complexity of ecological, social, and demographic factors.