A short note on extractive foraging behavior in gray snub-nosed monkeys.

Extractive foraging (EF) involves the exploitation of hidden or embedded foods, generally any food that is not visible to the naked eye. Therefore, EF is particularly important for survival in marginal habitats as it provides seasonal fallback foods in low food availability seasons. Although many studies consider primates' EF behavior and category, colobine species are usually categorized as non-extractive foragers and few studies quantitatively examine their EF behavior. In this study, we examined the EF behavior of one colobine species, the gray snub-nosed monkey (Rhinopithecus brelichi), at Yangaoping in Fanjingshan National Nature Reserve, Guizhou. We recorded 6 categories of EF behaviors. The most frequently sought-out foods were seeds, young bamboo and invertebrates. Extracted foods accounted for an average of 26.02% of feeding records. As the monkey engages in little EF behavior in the winter when the food availability is low, these results seem to do not support the hypothesis that EF serves to secure additional resources during lean times in marginal or seasonal habitats. According to these findings, we suggest R. brelich should be considered as an extractive forager. Our study also highlights the need for increased representation of colobines in the EF literature to better inform the discussion concerning its link to primate brain evolution.