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Saguinus fuscicollis illigeri was studied intermittently over a period of 5 years. Quantitative data on the diet, habitat use, ranging, and daily activities of one focal troop were gathered between November 1979 and January 1982. Modal troop size was 6 independently moving animals (observed range: 2–10). Troop size fluctuated over time, largely due to subadult/adult emigrations and immigrations. Population density was 15 animals/km 2 . Births occurred year-round, but a clear-cut peak season extended from December to March. The study troop occupied a defended home range of 15.7–16.5 ha. Treefall habitat was preferred over all other habitat types, and only 27% of the daytime was spent in non-edge tall-forest habitat. The troop spent 82% of the daytime in the lower forest strata (50% in the shrub stratum), below 11 m, and only 2 % in the highest stratum, above 20 m. Daily path length averaged 1,405 m. Daily ranging pattern showed seasonal changes related to seasonal fluctuation of fruit availability. Daily activities consisted of insect foraging (45 %), resting and grooming (32%), feeding on plant resources (14%), travel (6%), watching (2%), and others (1 %). Fruits, plant exudate, nectar, arthropods, frogs and lizards comprised the principal food resources. Fruit was the most important plant food, except during the peak dry season when 58% of plant-feeding time was spent consuming exudate. Nectar was an important resource in the early dry season. Bachelor groups of Saimiri boliviensis associated frequently with the study troop, and Saimiri was the most important resource competitor. The tamarins showed strong and consistent avoidance behavior towards Cebus apella.
Pekka Soini (Sat,) studied this question.