Patterns of aggression in spider monkeys (Ateles geoffroyii yucatanensis) at Runway Creek Nature Reserve, Belize

Abstract

“Patterns of aggression in spider monkeys (Ateles geoffroyii yucatanensis) at Runway Creek Nature Reserve, Belize” K. Hartwell¹, H. Notman1, 2, & M.S.M. Pavelka¹ ¹University of Calgary, Calgary, Alberta, Canada ²Athabasca University, Alberta, Canada Presenter’s Email: kaylahartwell@gmail.com

A number of studies looking at aggression in Ateles describe high rates of both male aggression directed at females (female-directed aggression by males, or M-FDA), as well as female aggression toward other females (or F-FDA). M-FDA may be an expression of feeding competition, direct sexual coercion, or indirect sexual coercion, and F-FDA may function to limit scramble competition. We collected detailed data on all observed incidences of aggression (N=193) in two spider monkey communities between January 2008 and August 2011. Of these, 154 were instances of M-FDA, and 29 incidents were F-FDA. Oneway ANOVA shows that adult and subadult males are significantly more likely to initiate aggression, and that subadult females are the most common targets. In instances of F-FDA, subadult females were the targets in 53% of the cases. Nonparametric tests show that contexts of aggression differed between M-FDA and F-FDA; M-FDA occurred most often during subgroup fusions (males joining subgroups containing females who were not feeding) and during feeding (37% and 31% respectively, N = 154); in contrast, F-FDA aggression rarely occurred during fusions but was more likely during feeding (14% and 41% respectively, N=29). Our results support the hypothesis that M-FDA is a form of indirect sexual coercion, and as a result may encourage sexual segregation as females try to avoid potentially aggressive males.