DOI: 10.25349/d91891
title: Wins and Losses in Intergroup Conflicts Reflect Energy Balance in Red-Tailed Monkeys

description: 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.
description: We collected the
 data for this analysis as part of a broader study on intergroup conflict
 in six neighboring groups of red-tailed monkeys from January 2012 through
 June 2015. All mature animals are individually recognized using the shape
 of the white nose spot, nipple characteristics (for females), and scars or
 other injuries. We followed 2-3 groups simultaneously for 1-2 weeks each
 month for multi-month periods (mean 4.9 ± SD 1.1 months, N = 7 periods),
 with 11-17 months between successive periods for a group. On every follow
 day, 2-4 observers tracked each group from dawn until dusk and noted the
 presence or absence of each individual, as well as whether each female was
 carrying and nursing an infant. We recorded the location of the group
 every 30 min as the point around which the majority of group members were
 clustered; we determined location using a 50 x 50 m gridded map of the
 trail system and by pacing to the nearest trails, or by using a hand-held
 GPS unit and later converting the UTM coordinates to the grid cell format.
 We recorded all foraging activity by group members during a 5 min window
 every half hour, including the plant species and part
 eaten. Observers recorded details of
 intergroup encounters, which we define as periods when the edges of two
 groups are ≤ 50 m apart, using a pre-printed template to ensure
 consistency across observers [17]. These details include the start and end
 times, the identity of the opposing group (if known), whether any chases
 or physical contact occurred between groups, and the location of the
 encounter. Observers spaced themselves out along the leading edge of the
 focal group as well as behind this edge in order to maximize our ability
 to track the events of these sometimes chaotic encounters. We also
 attempted to follow the opposing group for 60 minutes after the end of the
 encounter to track its movements. We collected fresh urine samples from
 mature individuals opportunistically throughout the day by pipetting
 droplets from low-lying vegetation immediately after excretion. We stored
 the samples on ice until 1700 hrs, at which time they were transferred to
 a -12°C freezer at the camp site. MB transported samples 1-2 times per
 year to the Hominoid Reproductive Ecology Laboratory at the University of
 New Mexico and we measured C-peptide levels with commercial
 radioimmunoassay kits (Millipore Sigma, Burlington, MA) using the
 manufacturer instructions. We defined four types of intergroup
 encounter outcome based upon the movements of the groups, relative to each
 other and/or to their pre-encounter travel direction [13, 14, 18].
 ‘Displacements’ occurred when one group (the winner) stayed in the IGE
 location for at least 30 min after the departure of the other, losing,
 group (N = 38 encounters). ‘Deflections’ occurred when both groups moved
 away after the encounter (N = 7), but the winner continued moving within
 45° of its original travel direction while the loser turned around to
 retreat into its home range. ‘Mutual avoid’ outcomes occurred when both
 groups turned around and retreated (N = 38), and ‘mutual ignore’ occurred
 when both groups continued moving forward (N = 1). Both displacements and
 deflections are considered ‘decided’ outcomes while mutual avoid and
 ignore are ‘draw’ outcomes. For each urine sample, we determined
 whether an intergroup encounter occurred on the same or following day; for
 those samples with an associated encounter, we calculated the difference
 between the time at which the sample was voided and the start of the
 encounter. Samples produced before and after an encounter had negative and
 positive values, respectively. We did not have enough urine samples from
 both interacting groups per encounter to compare their changes in
 C-peptide levels, so our analyses investigate general changes experienced
 by groups on days that they won, lost, or experienced a draw outcome. We
 also included samples from control periods: these were 2-day periods
 throughout the study in which we had collected multiple urine samples on
 each day, and in which there was no intergroup encounter. The control
 samples allowed us to determine the normal patterning of C-peptide
 responses and served as a useful comparison with the intergroup
 encounter-associated samples. To facilitate this comparison, we assigned a
 fake intergroup encounter number to each 2-day control period and
 designated the fake encounter start time as noon on the first day. This
 was a reasonable approximation because the encounters were approximately
 normally distributed around noon: 50% of encounters occurred before noon,
 and 41% occurred between 1100 and 1359 hrs.
description: See txt file with STATA code