The function of geophagy in Nepal gray langurs: Sodium acquisition rather than detoxification or prevention of acidosis.

OBJECTIVES: Geophagy has several hypothesized functions, among them (1) detoxification of plant secondary compounds, for example, tannins, (2) buffering stomach pH to alleviate acidosis caused by high sugar intake, and (3) supplementing the diet with mineral nutrients. We tested these hypotheses in Nepal gray langurs (Semnopithecus schistaceus), a foregut fermenter for which fruits and leaves dominate the diet at different times of the year. MATERIALS AND METHODS: We collected data on feeding time per food item for 21 unprovisioned adult langurs at Ramnagar, Nepal, for 1 year using instantaneous sampling (773 observation hours). We combined these data with relative sugar and tannin content of food items to estimate diet content. We collected rainfall data to distinguish the wet season (May-September) from the dry season (October-April). We collected soil samples from consumption and control sites to test for pH and sodium, potassium, magnesium, and calcium concentrations. RESULTS: Langurs consumed soil from two sources: termite structures (in almost all months) and river banks and beds (mainly in the dry season). Soil feeding was not positively correlated with dietary tannin or sugar content (GLMM). Soil pH was not high enough to buffer stomach contents. Only sodium was significantly higher in consumed soil. DISCUSSION: The most likely function of geophagy was the acquisition of sodium. This conclusion is consistent with reports for other animals. Buffering stomach pH, an often-suggested function for animals with ruminant-like digestion, was not supported. Detoxification, often proposed for animals with a diet high in secondary compounds, was also not supported.

Faecal Particle Size in Free-Ranging Proboscis Monkeys, Nasalis larvatus: Variation between Seasons.

Reducing the size of food particles is crucial for herbivores. Seasonal dietary changes are known to influence animals' chewing efficiency. Proboscis monkeys (Nasalis larvatus) are foregut fermenters, with a high chewing efficiency allowing them to achieve very fine faecal particles. In this study, we investigated how proboscis monkeys' chewing efficiency varies between wet and dry seasons, hypothesising differences possibly related to diet change. Faecal particle size analysis is an established approach to estimate chewing efficiency in mammalian herbivores. We analysed 113 proboscis monkey faecal samples collected in the Lower Kinabatangan Wildlife Sanctuary, between 2015 and 2017. By following standard sieve analysis protocols, we measured a mean particle size MPS0.025-8 of 0.45 ± 0.14 mm, and confirmed a previous result that proboscis monkeys have a very low faecal MPS. This study highlights a seasonal influence on proboscis monkeys' chewing efficiency, with smaller MPS (better chewing efficiency) during the wet season. During that time of the year, individuals may potentially change their diet, as all faecal samples contained intact seeds. Whether the seasonal MPS difference in proboscis monkeys is smaller than in other colobines due to their "rumination" strategy remains to be investigated.

Modifying the diets of captive proboscis monkeys in a temperate zoo to reduce weight loss and renal disease.

In animal husbandry, diets should help in maintaining a healthy body condition, support reproduction, and promote species-specific longevity. It is recommended to feed folivorous primates kept in zoos a high-fiber diet, i.e., leaves, although satisfying such a requirement is challenging in temperate regions because it is difficult to obtain fresh leaves, especially in autumn and winter. As equally important for their appropriate treatment, it is valuable to provide details of clinical reports of medical problems and pathological findings, although such clinical reports are rather limited. Therefore, in foregut-fermenting proboscis monkeys (Nasalis larvatus), we (1) described the individual clinical reports of renal disease and weight loss at the Yokohama Zoological Gardens in Japan, (2) determined the nutritional profile of the diets supplied to these animals because other potential triggers for their renal disease and weight loss could be excluded, (3) modified the diet regimen to minimize weight loss and the development of hypercalcemia and hypophosphatemia, and (4) assessed the effects of such dietary modification by comparing the body weight and the Ca and P concentrations and the Ca/P ratios in the blood before and after diet modification with a comparison of these measurements between zoo and free-ranging individuals. Based on the nutritional profile of the diets, we concluded that the reported cases of renal failure might be caused by consumption of leaves with a Ca/P ratio far above the appropriate level in autumn and winter. Additionally, the dietary modification of minerals and metabolizable energy achieved certain beneficial effects on zoo-kept proboscis monkeys.

The diet and feeding behavior of the black-and-white colobus (Colobus guereza) in the Kalinzu Forest, Uganda.

One of the goals for primate feeding ecology is to understand the factors that affect inter- and intra-specific variations. Therefore, a detailed description of basic feeding ecology in as many populations as possible is necessary and warrants further understanding. The black-and-white colobus (Colobus guereza) or guereza is widely distributed in Africa and is one of the well-studied colobines in terms of their feeding; they demonstrate considerable variation in their diets in response to local conditions. We studied the diet of a group of guerezas in the Kalinzu Forest, Uganda, for over 30 consecutive months using behavioral observation (4308 h in total), phenology, and vegetation surveys. A total of 31 plant species were consumed by the study group. This study group was predominantly folivorous; the majority of their feeding time was involved in feeding on young leaves (87%). However, during certain times of the year, fruits and seeds accounted for 45% of monthly feeding time. Young leaves of Celtis durandii were by far the most important food, which constituted 58% of the total feeding records. There was a significant increase in the consumption of fruits and flowers once young leaf availability was low, but their consumption of fruits did not significantly increase even when fruit availability was high. Their monthly dietary diversity increased as the number of available plants with young leaves declined, suggesting that much of the dietary diversity in the study group may be attributable to the young leaf portion of their diet. Our findings may help contribute to a better understanding of the dietary adaptations and feeding ecology of guerezas in response to local environmental conditions.

Primate Resting Postures: Constraints by Foregut Fermentation?

Although resting is one of the dominant behaviors of foregut-fermenting primates (i.e., colobines), their resting posture has rarely received attention. We hypothesize that colobines are more constrained in their resting position than hindgut-fermenting primates and that colobines assume a sitting resting position for specific reasons. To test this hypothesis, we followed two approaches. First, we observed resting positions in two captive individuals each of eight species and tested whether colobines rested in a sitting position more than other primates. Second, we collected literature data on free-ranging specimens of 31 species and again tested whether colobines rested in a sitting position more than other primates. Both approaches indicated that colobines spent more time in a sitting posture than other primates (73.0% vs. 23.2% in captivity and 83.0% vs. 60.9% in the wild, respectively). We hypothesize that the position of the digestive chamber and the necessity of frequently having to eructate digestion gases force colobines to take a sitting posture to avoid pressure on the thorax and respiratory organs.