Divergent strategies in faeces avoidance between two cercopithecoid primates

Sniffing behavior of semi free-ranging Barbary macaques (Macaca sylvanus)

Olfaction is one of the evolutionarily oldest senses and plays a fundamental role in foraging and social interactions across mammals. In primates, the role of olfaction is now well recognized, but better investigated in strepsirrhine and platyrrhine primates than in catarrhines. We observed the sniffing behavior of semi-free ranging Barbary macaques, Macaca sylvanus, at Affenberg Salem, Germany, to assess how frequently macaques sniff and in which contexts, and how sniffing is affected by sex and age. Focal observations of 24 males and 24 females aged 1-25 years showed that Barbary macaques sniffed, on average, 5.24 times per hour, with more than 80% of sniffs directed at food. Irrespective of the context, younger individuals sniffed more often than older ones. Females' sniffs were more often directed at food than male sniffs, while males sniffed more often than females in a social context. Sniffs at conspecifics occurred primarily in a sexual context, with 70% of social sniffs directed at female anogenital swellings performed by males. Of the observed 176 anogenital inspections, 51 involved sniffing of the swelling. Olfactory inspections were followed by copulation significantly less often than merely visual inspections, suggesting that anogenital odors may play a role in male mating decisions, but the role of olfaction in sexual interactions warrants further investigations. In sum, results show that Barbary macaques routinely use olfaction during feeding, but also in a socio-sexual context, corroborating the relevance of the olfactory sense in the lives of catarrhine primates.

Disgust in animals and the application of disease avoidance to wildlife management and conservation

Disgust is an adaptive system hypothesized to have evolved to reduce the risk of becoming sick. It is associated with behavioural, cognitive and physiological responses tuned to allow animals to avoid and/or get rid of parasites, pathogens and toxins. Little is known about the mechanisms and outcomes of disease avoidance in wild animals. Furthermore, given the escalation of negative human-wildlife interactions, the translation of such knowledge into the design of evolutionarily relevant conservation and wildlife management strategies is becoming urgent. Contemporary methods in animal ecology and related fields, using direct (sensory cues) or indirect (remote sensing technologies and machine learning) means, provide a flexible toolbox for testing and applying disgust at individual and collective levels. In this review/perspective paper, we provide an empirical framework for testing the adaptive function of disgust and its associated disease avoidance behaviours across species, from the least to the most social, in different habitats. We predict various trade-offs to be at play depending on the social system and ecology of the species. We propose five contexts in which disgust-related avoidance behaviours could be applied, including endangered species rehabilitation, invasive species, crop-raiding, urban pests and animal tourism. We highlight some of the perspectives and current challenges of testing disgust in the wild. In particular, we recommend future studies to consider together disease, predation and competition risks. We discuss the ethics associated with disgust experiments in the above contexts. Finally, we promote the creation of a database gathering disease avoidance evidence in animals and its applications.

Environmental and individual determinants of fecal avoidance in semi-free ranging woolly monkeys (Lagothrix lagotricha poeppigii)

OBJECTIVES

Parasite selection pressures have driven the evolution of numerous behavioral defenses in host species, but recent studies revealed individual variation in their expression. As little is known about the factors causing heterogeneity among individuals in infection-avoidance behaviors, we investigated in woolly monkeys (Lagothrix lagotricha poeppigii) the influence of several environmental and individual characteristics on the tendency to avoid food contaminated by soil and by their own and conspecifics' feces.

MATERIALS AND METHODS

We conducted feeding tests on 40 semi-free ranging individuals rescued from the pet trade. Using generalized linear mixed models, we investigated the effect of season, sex, age, dominance rank, and exposure to non-natural living conditions on feeding decisions.

RESULTS

Woolly monkeys did not avoid soil-contaminated food and equally avoided food contaminated by their own and conspecifics' feces. Individuals varied greatly in their level of fecal avoidance. Only females exhibited strong avoidance of fecally contaminated food, but adapted their behavior to food availability, highlighting the trade-off between nutritional intake and parasite avoidance. Additionally, low-ranking females, less competitive over food resources, exhibited lower avoidance than dominant ones. Juveniles were more cautious than adults, possibly to compensate for a higher parasite susceptibility. Finally, we reported an unknown effect of exposure to non-natural living conditions on behavioral defenses, as animals kept as household pets for an extended period apparently lost their ability to avoid fecally contaminated food.

CONCLUSION

We argue that striving to understand variation in infection-avoidance behaviors in natural populations is crucial to predict disease spread and inform conservation policies.

Selecting between iron-rich and clay-rich soils: a geophagy field experiment with black-and-white colobus monkeys in the Budongo Forest Reserve, Uganda

Geophagy, the intentional consumption of soil, has been observed in humans and numerous other animal species. Geophagy has been posited to be adaptive, i.e., consumed soil protects against gastrointestinal distress and/or supplements micronutrients. We conducted a field experiment in the Budongo Forest, Uganda, to investigate geophagic behaviors, including soil preference, the quantity of soil eaten, and competition for access to preferred soils. We placed pairs of artificial tree stumps at two existing geophagy sites. One stump contained soil from the surrounding area, Sonso, that could supplement bioavailable iron. The other stump contained soil from a neighboring community, Waibira, that was richer in clay minerals, which could provide protection from plant secondary compounds. We monitored activity and engagement with the stumps for 10 days using camera traps. After 5 days, we reversed the type of soil that was in the stumps at both sites (i.e., a crossover design). Only Colobus guereza (black-and-white colobus monkeys) interacted with the stumps. These monkeys used visual and olfactory cues to select between the two soils and exclusively ate the clay-rich soil, consuming 9.67 kg of soil over 4.33 h. Our findings lend the greatest plausibility to the protection hypothesis. Additionally, monkeys competed for access to the stumps, and 13% of the videos captured aggression, including pushing, excluding, and chasing other individuals from the experimental stumps. Nine episodes of vigilance and flight behavior were also observed. Given that intentionally ingested soil is a valuable resource that may confer health benefits, geophagy sites should be conserved and protected.