Competition for resources and the need for cooperation are reported to affect patterns of social interactions and thus the quality of social relationships in primates. Relationships may be described as high quality when both individuals behave in a way that benefits their partner. We investigated the distribution of a wide range of social behaviors across sex partner combinations of adult spider monkeys with specific reference to contested resources. Data were collected from two communities of wild spider monkeys (Ateles geoffroyi yucatanensis) in the Otoch Ma'ax Yetel Kooh reserve in Yucatan, Mexico. Affiliative behavior was exchanged most frequently between males, and as male-male aggression was rare, male-male social relationships were characterized as high quality. Female-female social relationships were best described as low quality as females showed no preference to be in proximity with other females and female-female affiliative behavior was rare. Relationships between the sexes generally were characterized by high rates of female-directed male aggression, although additional investigation into the effects of kinship and female reproductive state on male-female relationships is required before further conclusions can be drawn. Dyadic and coalitionary female-female aggression was significantly higher than expected in a feeding context, confirming that female spider monkeys primarily compete for access to food. Male-male aggression did not increase significantly when in the presence of females, but males embraced at higher rates when in mixed-sex subgroups. As embraces serve to reduce the likelihood of aggression during tense situations, high rates of male-male embraces in mixed-sex subgroups may mitigate male conflicts over access to females.

Threats to biodiversity are well documented. However, to effectively conserve species and their habitats, we need to know which conservation interventions do (or do not) work. Evidence-based conservation evaluates interventions within a scientific framework. The Conservation Evidence project has summarized thousands of studies testing conservation interventions and compiled these as synopses for various habitats and taxa. In the present article, we analyzed the interventions assessed in the primate synopsis and compared these with other taxa. We found that despite intensive efforts to study primates and the extensive threats they face, less than 1% of primate studies evaluated conservation effectiveness. The studies often lacked quantitative data, failed to undertake postimplementation monitoring of populations or individuals, or implemented several interventions at once. Furthermore, the studies were biased toward specific taxa, geographic regions, and interventions. We describe barriers for testing primate conservation interventions and propose actions to improve the conservation evidence base to protect this endangered and globally important taxon.

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Male spider monkeys direct the majority of their aggression toward adult females, and the aggressive interactions may be a form of sexual coercion. We investigated female-directed male aggression in 2 wild communities of spider monkeys (Ateles geoffroyi yucatanensis) from the Otoch Ma'ax Yetel Kooh Reserve in Yucatan, Mexico to evaluate the sexual coercion hypothesis. The aggression occurred in 2 distinct forms: physical aggression and prolonged noncontact chases. The latter appeared highly ritualized in nature and accounted for >80% of all femaledirected male aggression. Rates of prolonged chases, but not physical aggression, peaked when the female target was likely cycling and were associated with male place-sniffing of the substrate previously occupied by the female target. Prolonged chases were also associated with proceptive behavior directed from the female target toward her male attacker after the chase had ceased. Our data therefore suggest that prolonged chases are sexually motivated. Prolonged chases did not result in immediate copulation, but sometimes the female victim left the subgroup to travel alone with her male aggressor, and thus prolonged chases may be a form of male intimidation to coerce females into a mating consortship. However, as prolonged chases appeared highly ritualized, the chases may also be a form of male sexual display. Further investigation of the costs incurred by female recipients of prolonged chases is therefore required before one can interpret the behavior as sexual coercion.