To understand the effects of the chemical and physical properties of plant leaves on food choice in Rhinopithecus bieti,we collected mature leaves of nine food and five non-food plant species at the southernmost part of the species's range.Chemical properties such as fat, ash, crude protein (CP), total phenolics (TP), and fiber content including neutral detergent fiber(NDF), acid detergent fiber (ADF), lignin, celluloses and hemicelluloses, and physical toughness were measured. R. bieti tendedto choose leaves with lower fiber content, higher ash, a higher ratio of CP/ADF, and lower toughness. No difference was foundfor fat, crude protein, total phenolics, hemicelluloses and lignin between food and non-food leaves. Even though the ratio ofCP/ADF is generally regarded as a good indicator for colobine food choice, the difference in the ratio of CP/ADF between foodand non-food leaves was only the result of differences in ADF. Since positive correlations were found between ADF and toughnessfrom all leaves (both food and non-food species), and toughness of leaves was likely easier for R. bieti to sense than fibercontent via mastication, the toughness of leaves may function as a predictor of food choice in this species.
