Wins and Losses in Intergroup Conflicts Reflect Energy Balance in Red-Tailed Monkeys

The energetic costs and benefits of intergroup conflicts over feeding
sites are widely hypothesized to be significant, but rarely quantified. In
this study, we use short-term measures of energy gain and expenditure to
test whether winning an intergroup encounter is associated with greater
benefits, and losing with greater costs. We also test an alternative
perspective, where groups fight for access to large food sources that are
neither depletable nor consistently monopolizable: in this case, a group
that has already fed on the resource and is willing to leave first (the
loser) is supplanted by a newly arrived group (the winner). We evaluate
energy balance and travel distance during and after encounters for six
groups of red-tailed monkeys in Kibale National Park, Uganda. We find that
winning groups experience substantial energetic benefits, but do so to
recoup from earlier deficits. Losing groups, contrary to predictions,
experience minimal energetic costs. Winners and losers are predictable
based upon their use of the contested resource immediately before the
encounter. The short-term payoffs associated with these stressful
conflicts compensate for any associated costs and support the perception
that between-group contests are an important feature of social life for
species that engage in non-lethal conflicts.