Digestion of selected foods by Yunnan snub-nosed monkey Rhinopithecus bieti (Colobinae).

Three digestion trials were conducted to quantify aspects of digestive physiology in the Yunnan snub-nosed monkey Rhinopithecus bieti, a foregut fermenter that feeds primarily on lichens. Mean retention time (MRT, the average time plastic markers spent in the animal) had a mean estimate of 47 hr (n = 3) with high variability between trials (standard deviation = 17 hr). Recently captured animals, presumably with gut flora and digestive physiology close to wild animals, had a longer retention time than did long-term captives, although lack of standardization across trials (such as in activity level) confounds analysis. Apparent digestibilities for dry matter (71-80%) were in line with other studies of colobine digestion, but fall below those of ruminant ungulates feeding on lichens. Fecal analysis accurately determined the relative proportions of leaves vs. lichens in diets; mature leaves and lichens were not nutritional equivalents but appeared to be physiological equivalents in terms of digest passage. Fecal analysis does not, however, accurately determine the relative proportions of food types with different digestibilities, such as fruit vs. leaves.