The Ecology and Behavior of the Rio Mayo Titi Monkey (Callicebus Oenanthe) in the Alto Mayo, Northern Peru

I document the behavior and ecology of a small pair-bonded primate, the Río Mayo or Andean titi monkey ( Callicebus oenanthe ). This is the first long-term field study on this endangered primate. Research was conducted in a 3-hectare forest patch found near the Río Mayo, San Martin, Peru, at 890 meters a.s.l. The study group, consisting of an adult pair and two offspring, was observed for over 800 hours from January to August 2005 using instantaneous focal sampling. The titi monkeys spent a majority of the time acquiring and ingesting fruits and insects (\u3e80%), with lesser portions of leaves, tendrils, meristems, flowers, and young seeds. Few fruit species contributed to the majority of the fruit diet, and 1 to 2 species made up the majority of the diet per month. Time devoted to insect foraging represented a considerable portion of daily activity budget (17%). C. oenanthe is mainly an investigative forager of immobile insects and spiders but also opportunistically caught fast-moving insects and fed on mass congregations of insects. During resource scarcity C. oenanthe switched its diet to mostly insects and flowers, used different plant parts, and relied on plant resources that were either common in disturbed forest habitat or were available for extended periods of time, such as fruits from semi-parasitic mistletoes. The female consumed more insects than the male, especially during lactation. The male spent the majority of time resting, and resting increased significantly during the infant carrying period. Although the male and female exhibited characteristics typical of a strong pair bond, the male contributed more to grooming bouts, was responsible for a greater proportion of contacts made, and closely followed the female more than the reverse. Sex differences in energetic requirements as seen by differences in the amount and type of insect foraging and activity may have led to the variation observed in the investment in the pair bond. Divergent mechanisms maintaining the pair bond and the ability to exploit a variety of food types, as well as other differences from previously-studied species of Callicebus suggests that this genus is more socially and behaviorally flexible than previously thought