Feeding behavior and aggression in wild Siberut macaques (Macaca siberu) living under low predation risk

Cofeeding at rich clumped food patches in free-ranging dogs: social tolerance or scramble competition?

Abstract

Animals are generally expected to monopolize food patches whenever possible. However, cofeeding within a defendable range occurs in many species, particularly at larger food patches, but the mechanism behind that remains underexplored. In theory, it could be due to multiple, mutually non-exclusive processes. First, larger food patches may saturate multiple top-ranking individuals, enabling cofeeding even under pure contest competition. Second, cofeeding may result from social tolerance where dominant individuals provide cofeeding concessions to certain subordinates. Third, cofeeding may result from prevailing scramble competition (i.e., indirect competition through patch exploitation) caused by large numbers of individuals that prevent monopolization ("swamping"). To investigate and differentiate between these mechanisms, we applied feeding tests to free-ranging dogs in Morocco. We provided them with a large food patch plus a varying number of small food patches. Although the small food patches were virtually always monopolized by single individuals, the dogs typically cofed in large and very dense feeding groups at the large food patches. Controlling for alternative explanations using multivariate statistics, we found that access to feeding groups was independently predicted by rank and social relationship strength, suggesting that contest competition and social tolerance play a role. However, aggression rates by top-rankers decreased with increasing feeding group size, suggesting decreasing monopolizability and increasing scramble competition. Our results underscore that social tolerance may not reduce competition but shifts it from contest to scramble competition. This can be due to active levelling, licensing more individuals access to the resource, but also to loss of control caused by swamping.

Significance statement

Although animals are generally expected to fight for resources, they are sometimes observed to cofeed peacefully in large groups. Such peaceful cofeeding is typically ascribed to and taken as a measure of social tolerance, assuming that dominants overcome their impulse to monopolize and make concessions to lower-ranking group members. Alternatively, such large peaceful cofeeding groups may result from swamping where lower-ranking group members overrun dominants as a mob. In this scenario, the dominant individuals simply lose control. Fighting would be pointless and only make them lose feeding time and reduce their share while others are feeding. Studying feedings of free-ranging dogs, we show that aggression by dominants decreases with increasing feeding group size, which supports this alternative explanation and sheds new light on the emergence of cofeeding and social tolerance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00265-025-03590-8.

Development of an assessment method for freely moving nonhuman primates' eating behavior using manual and deep learning analysis

Purpose

Although eating is imperative for survival, few comprehensive methods have been developed to assess freely moving nonhuman primates' eating behavior. In the current study, we distinguished eating behavior into appetitive and consummatory phases and developed nine indices to study them using manual and deep learning-based (DeepLabCut) techniques.

Method

The indices were utilized to three rhesus macaques by different palatability and hunger levels to validate their utility. To execute the experiment, we designed the eating behavior cage and manufactured the artificial food. The total number of trials was 3, with 1 trial conducted using natural food and 2 trials using artificial food.

Result

As a result, the indices of highest utility for hunger effect were approach frequency and consummatory duration. Appetitive composite score and consummatory duration showed the highest utility for palatability effect. To elucidate the effects of hunger and palatability, we developed 2D visualization plots based on manual indices. These 2D visualization methods could intuitively depict the palatability perception and hunger internal state. Furthermore, the developed deep learning-based analysis proved accurate and comparable with manual analysis. When comparing the time required for analysis, deep learning-based analysis was 24-times faster than manual analysis. Moreover, temporal and spatial dynamics were visualized via manual and deep learning-based analysis. Based on temporal dynamics analysis, the patterns were classified into four categories: early decline, steady decline, mid-peak with early incline, and late decline. Heatmap of spatial dynamics and trajectory-related visualization could elucidate a consumption posture and a higher spatial occupancy of food zone in hunger and with palatable food.

Discussion

Collectively, this study describes a newly developed and validated multi-phase method for assessing freely moving nonhuman primate eating behavior using manual and deep learning-based analyses. These effective tools will prove valuable in food reward (palatability effect) and homeostasis (hunger effect) research.

Investigating the dietary niches of fossil Plio-Pleistocene European macaques: The case of Macaca majori Azzaroli, 1946 from Sardinia

The genus Macaca includes medium- to large-bodied monkeys and represents one of the most diverse primate genera, also having a very large geographic range. Nowadays, wild macaque populations are found in Asia and Africa, inhabiting a wide array of habitats. Fossil macaques were also present in Europe from the Late Miocene until the Late Pleistocene. Macaques are considered ecologically flexible monkeys that exhibit highly opportunistic dietary strategies, which may have been critical to their evolutionary success. Nevertheless, available ecological information regarding fossil European species is very sparse, limiting our knowledge of their evolutionary history in this geographic area. To further our understanding of fossil European macaque ecology, we investigated the dietary ecology of Macaca majori, an insular endemic species from Sardinia. In particular, we characterized the dental capabilities and potential dietary adaptations of M. majori through dental topographic and enamel thickness analyses of two M2s from the Early Pleistocene site of Capo Figari (1.8 Ma). We also assessed its diet through dental microwear texture analysis, while the microwear texture of M. majori was also compared with microwear textures from other European fossil macaques from mainland Europe. The dental topographic and enamel thickness analyses suggest that M. majori frequently consumes hard/mechanically challenging and/or abrasive foods. The results of the dental microwear analysis are consistent with this interpretation and further suggest that M. majori probably exhibited more durophagous dietary habits than mainland Plio-Pleistocene macaques. Overall, our results indicate that M. majori probably occupied a different dietary niche compared to its mainland fossil relatives, which suggests that they may have inhabited different paleoenvironments.

Social Network Analysis as a Tool in the Care and Wellbeing of Zoo Animals: A Case Study of a Family Group of Black Lemurs (Eulemur macaco)

Social network analysis (SNA) is an increasingly utilised technique in the literature examining the social structures and organisation of animals and understanding the bonds between groups and individuals. Using a case study as an illustration, the applications of SNA are explored, including the identification of dominance hierarchies and detection of sources of social pressure, with a particular focus on the applications of SNA to holistic assessments of animal welfare alongside other methods. Based on the examination of social dynamics in a family group of four black lemurs (Eulemur macaco), a primate whose social organisation is characterised by patterns of female dominance, it is demonstrated that SNA can be used to examine the affiliative and agonistic interactions between individuals living in human care. SNA showed species-typical forms of female dominance that were largely directed towards the two males, characterised by the initiation of aggressive interactions and male submission. More intricate relationships and consistent social roles across networks were revealed through the examination of SNA. It is concluded that SNA has wide-ranging benefits in the assessment of effects of environmental changes, such as informing social management decisions, developing enrichment and intervention programs, and guiding overall improvements to the housing and care of individual animals. SNA, as part of an animal welfare toolbox, could, therefore, be a pivotal technique for modern animal welfare assessment that considers individual animals and their social lives. By sharing a case study of the technique in use, it is hoped that animal collections may adopt similar modern and evidence-based assessment methods.