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Animals that occupy stable home ranges tend to unevenly exploit different areas in their efforts to find fitness-limiting resources, while also reducing the risks of intergroup conflict. Most analyses of these extrinsic forces identify their effects on movement paths and home range geometry, but not on the interaction of these responses or how movements might be centrally constrained as a result of competition with neighbors. The range utilization slope is a measure of central tendency and consists of space use plotted against distance from the center of the range. Slopes tend to be linear, concave-up, or concave-down and are predicted to change as a function of feeding competition from neighbors. To test this prediction and determine the spatio-temporal scales over which the central tendency might vary, we calculated utilization slopes and an index of range overlap for grey-cheeked mangabeys (Lophocebus albigena), blue monkeys (Cercopithecus mitis), and red-tailed monkeys (C. ascanius) in Uganda, which consume similar diets but experience varying intensities of intergroup conflict. As predicted, we find variation in utilization slopes across and within species, which corresponds with the extent of range overlap among conspecific groups. 

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. This article is part of the theme issue ‘Intergroup conflict across taxa’. 

Abstract Changes in population size are driven by environmental and social factors. In spite of repeated efforts to identify the constraints on an unusually low-density population of blue monkeys ( Cercopithecus mitis ), it remains unclear why this generalist species fails to thrive in Kibale National Park in Uganda. While an unidentified disease may occasionally obstruct conception, it does not seem to limit overall reproductive rates. Infanticide at this site is infrequent due to the long tenures of resident males. Our analyses indicate that the single biggest constraint on blue monkey densities may be feeding competition with grey-cheeked mangabeys ( Lophocebus albigena ): across Kibale, the densities of these two species are strongly and negatively correlated. Though further analysis is needed to understand the timing and strength of feeding competition between them, we conclude that blue monkeys at Ngogo experience competitive exclusion from grey-cheeked mangabeys, possibly resolving the 50-year mystery surrounding this population. 

Orangutans have a 7.6 year average inter-birth interval, the longest of any mammal. Suckling occurs throughout that interval, until the birth of the next offspring, but it is unclear how important milk consumption is during that period, as we cannot assess the actual intake amount. Measurement of stable carbon isotope ratios (d13C), stable nitrogen isotope ratios (d15N) and nitrogen content of feces (%N) provide evidence of the transition between breast milk to solid food. Here we present pilot data on these isotopic ratios from matched fecal samples of mothers and offspring (n=43), collected from wild orangutans in Gunung Palung National Park, Borneo, Indonesia. We found that the youngest infant (2.3 yrs) had the highest d15N values overall, indicative of a higher percentage of animal products (milk) in the diet. Older juveniles (5.8 yrs) did not consistently show higher d15N than their mothers. This may indicate variation in suckling frequency or the amount of breast milk consumed per suckling session. Adolescents (10-13 yrs) showed significantly (GLMM, p< 0.007) lower d15N than samples taken from the same day on their mothers. This is surprising given that they were eating similar diets. We thus compare the isotopic signature of the plants consumed to examine the sources of this variation. We conclude that analysis of fecal samples collected from wild orangutans can be used to assess the relative importance of breast milk in the diet, but caution that isotopic excretion may also be effected by differences in the isotopic content of the diet. Funders: NSF (BCS-1638823, BCS-0936199); National Geographic; USFish/Wildlife (F15AP00812, F13AP00920, 96200-0-G249, 96200-9-G110); Leakey; Disney Wildlife Conservation; Wenner-Gren; Nacey-Maggioncalda; Orangutan Conservancy; Conservation-Food-Health; Woodland Park Zoo; Holloman Price; AZA; Ocean Park Conservation; USAID; Arcus 

The Gunung Palung Orangutan Project has conducted research on critically endangered wild Bornean orangutans (Pongo pygmaeus wurmbii) since 1994 in Gunung Palung National Park, West Kalimantan, Indonesia. A major goal of our broad-ranging research on orangutan behavior and ecology is to understand how the unique rainforest environment of Southeast Asia, characterized by dramatic changes in fruit productivity due to unpredictable mast fruiting, impacts orangutan behavior, physiology, and health. Much of our research has been devoted to the development of non-invasive techniques and an integrated biology approach – using hormonal assays, fecal processing, nutritional analysis, genetics, and behavioral ecology – and has led to an increased understanding of the ecological and evolutionary pressures shaping orangutan adaptations. Our results show that the extended life history and very slow reproductive rate of orangutans are adaptations to their environment. Orangutans in the Gunung Palung landscape, as elsewhere across Borneo and Sumatra, also face a series of conservation challenges, including extensive habitat loss and the illegal pet trade. We highlight how our investigations of orangutan health status, ecosystem requirements, and the assessment of orangutan density using ground and drone nest surveys have been applied to conservation efforts. We describe our project’s direct conservation interventions of public education and awareness campaigns, sustainable livelihood development, establishment of village-run customary forests, investigation of the illegal pet trade, and active engagement with Indonesian government organizations. These efforts, in concert with the development of local scientific and conservation capacity, provide a strong foundation for further conservation as orangutans face a challenging future. 

Animal communication has long been thought to be subject to pressures and constraints associated with social relationships. However, our understanding of how the nature and quality of social relationships relates to the use and evolution of communication is limited by a lack of directly comparable methods across multiple levels of analysis. Here, we analysed observational data from 111 wild groups belonging to 26 non-human primate species, to test how vocal communication relates to dominance style (the strictness with which a dominance hierarchy is enforced, ranging from ‘despotic’ to ‘tolerant’). At the individual-level, we found that dominant individuals who were more tolerant vocalized at a higher rate than their despotic counterparts. This indicates that tolerance within a relationship may place pressure on the dominant partner to communicate more during social interactions. At the species-level, however, despotic species exhibited a larger repertoire of hierarchy-related vocalizations than their tolerant counterparts. Findings suggest primate signals are used and evolve in tandem with the nature of interactions that characterize individuals' social relationships.