Multiple resource values and fighting ability measures influence intergroup conflict in guerezas ( Colobus guereza)

Abstract

Intergroup conflict occurs in many social species and involves potentially complex motivations and interactions. To understand its complexity in wild animals more fully, a comprehensive investigative approach is needed, in which the multiple resource values and measures of fighting ability that potentially influence intergroup contests are simultaneously considered and controlled for. This study uses long-term data on eight neighbouring groups of folivorous black and white colobus monkeys, Colobus guereza (‘guerezas’) in Kibale National Park, Uganda, to investigate the factors influencing intergroup conflict. Adult males were the main participants in intergroup aggression. Of the three resource values investigated, food value had the most unambiguous positive effect on the tendency for males to initiate high-level intergroup aggression and for groups to win. Mate value positively influenced male initiation of high-level intergroup aggression, but not more so for the group that contained high-value mates. The presence of young infants had no obvious effects. Unlike in many other species, males were more likely to initiate intergroup aggression if their groups were smaller and contained fewer adult males than opposing groups. Groups with fewer but larger adult males, and to some extent, smaller groups, were more likely to win encounters. Moreover, the relative number of adult males/group largely affected the degree to which some other factors influenced male initiation of aggression and contest outcome. These findings reveal that a complex interplay between multiple resource values and multiple fighting ability measures can simultaneously influence initiation of and success in intergroup conflict.