Interactions of Howler Monkeys with Other Vertebrates: A Review

TLDR: An extensive search of the available data on interspecific howler encounters, including individual communications from field primatologists, is completed in order to gain insight into how howlers share their habitat and interact with other species, the pressure that predators and potential competitors may exert on them, and the potential benefits and costs that howlers may represent for other species.

Abstract: Understanding the way howler monkeys interact with other vertebrates has critical ecological, evolutionary, cognitive, and conservation implications. In this review, we completed an extensive search of the available data on interspecific howler encounters, including individual communications from field primatologists, in order to gain insight into how howlers share their habitat and interact with other species, the pressure that predators and potential competitors may exert on them, and the potential benefits and costs that howlers may represent for other species. Howlers interacted with several vertebrates throughout their distribution range, including birds and mammals, particularly capuchin monkeys, spider monkeys, and coatis. A great deal of these interactions occurred in fruiting trees and were, in general, pacific, although howlers were frequently harassed by other monkeys, and they were observed behaving aggressively with coatis and birds. Howlers were also targets of multiple predators. Among them, large felids and harpy eagles are ranked as the prevalent natural predators of this primate taxon. Finally, evidence indicates that the transformation of natural habitats can have important effects on the interaction patterns of howlers with other species. Fragmentation can increase competition for food and in extreme cases even force them to predate on eggs to compensate for the reduction in food availability. On the other hand, natural predators are often absent in anthropogenic landscapes, but there are increasing reports of predation by dogs and coyotes, which could potentially have very negative effects on the already highly threatened populations of howler monkeys in fragmented landscapes.