Seasonal Ecological Flexibility of a Threatened Bolivian Endemic: Olalla's Titi Monkey (plecturocebus Olallae)

In the face of reduced food availability, primates must choose between expending energy to look for adequate foraging options, or saving energy by reducing activity and intake requirements. In a 1-year study of two groups of Olalla’s titi monkey (Plecturocebus olallae) in the fragmented forests of the Llanos de Moxos, Bolivia, we assessed seasonal variations in behavior, ranging, and diet to examine their ecological flexibility. We observed groups in the wet and dry seasons, recording behavior with instantaneous group scan sampling (743.5 observation hours in the dry season and 733.0 hours in the wet season) and ranging and feeding data with all occurrence sampling. At the same time, we collected data on food availability via monthly phenology monitoring. The titi monkeys fed mainly on fruits and significantly reduced the time they spent consuming fruit during the dry season compared with the wet season while showing some (nonsignificant) increase in their consumption of leaves, and other foods (seeds, lichens, and fungi). Home ranges remained relatively constant, but titi monkeys spent less time moving in the dry season than in the wet season, although this difference was not significant. The observed shift in diet toward consuming alternative foods during the fruit lean period and reducing movement instead of expanding ranging behavior to look for higher-quality foods suggests that P. olallae follows an energy–area minimizing strategy that may enable these primates to inhabit fragmented forests. Nevertheless, deforestation and further fragmentation in the range of these endemic and Critically Endangered primates must be addressed, as they represent significant threats to the severely range-restricted P. olallae populations. Our study illustrates the relevance of understanding primate ecological flexibility in response to food reductions to the development of conservation actions, especially in the light of increasing forest degradation and loss in the study region.