Feeding Ecology of the Beni Titi Monkey (Plecturocebus modestus): An Endangered Bolivian Endemic

Primates can respond to food availability shortages by increasing the energy they invest in searching for alternative food resources or by conserving energy by altering their diet while reducing movement. To gain information on the ecological flexibility of Beni titi monkeys (Plecturocebus modestus), we assessed seasonal variation in the behavior and ranging and feeding patterns of two focal groups across a year. We recorded group behaviors using instantaneous group scan sampling and used all occurrence sampling to collect ranging and feeding data (1,178 observation hours in the dry season, and 1,202 in the wet season). We collected data on food availability via monthly phenology monitoring. We found that during the fruit-scarce dry season, these frugivorous primates significantly reduced their monthly investment in moving and increased their consumption of flowers. They also showed some decrease in fruit consumption, home ranges and daily path length. Our observations of a diet shift to a high intake of alternative foods and reduction of time spent on moving suggest that the P. modestus groups that we studied used an energy-area minimizing strategy when fruits were less available. While we found that P. modestus could find food in the naturally fragmented forests, high levels of ongoing anthropogenic forest fragmentation may lead to reductions in important food resources, threatening the survival of these Endangered primates. This study shows the ecological flexibility of primates and provides important information to be incorporated in the design of specific effective conservation actions for this threatened an endemic species, as well as highlights the importance of mitigating the current threats to these forest ecosystems.