Interspecific and integroup interactions of mantled howling monkeys (Alouatta palliata) in primary versus secondary forest at El Zota Biological Field Station, Costa Rica

Four groups of mantled howling monkeys (Alouatta palliata) were observed at El Zota Biological Field Station in northeastern Costa Rica to assess whether resource scarcity caused by anthropogenic disturbance and hypothesized increased competition for limited resources would result in more frequent and more aggressive interactions between neighboring howling monkey groups and between howling monkeys and other, sympatric primate species, namely white-faced capuchins (Cebus capucinus) and black-handed spider monkeys (Ateles geoffroyi). Using a comparison between the primary forest, as a control, and anthropogenically-altered secondary forest, I examined whether a behavioral difference existed between groups with hypothesized varying degrees of resource competition. Intergroup encounters were broken down into long distance howling bouts, with 46 observed, and close proximity interactions, with 11 observed. Results showed an increased frequency of howling in the primary forest as compared with the secondary forest, but no difference between the frequency, duration, or type of close-proximity intergroup encounters. Forty-five interspecies interactions were observed between howling monkeys and sympatric primate species. These interactions showed no difference between forest type for frequency, duration, or type of interaction. These results suggest that the composition and resource availability of the secondary forest at this site that does not align with current assumptions of habitat degradation. Alternatively results may be a reflection of social pressures such as infanticide, intragroup competition, and genetic relatedness as factors shaping howling monkey behaviors in both primary and secondary forests.