Abstract
A 5 month field study was conducted in the Pando Department of northern Bolivia, on two tamarin species: the red-bellied tamarin, Saguinus l. labiatus, and the saddle-back tamarin, S. fuscicollis weddelli. Data were collected both by observation and radio-location on the group sizes, ranging behavior, daily activity patterns, and intergroup interactions. The two tamarin species formed stable mixed associations and each mixed species troop shared a common home range which they jointly defended against neighboring mixed species troops. Both species appeared to occupy a similar ecological niche, but differences were highlighted in their methods of insect foraging, their preferred height in the forest, and their mode of travel.