To estimate population density near Huaisi a rectangular area of 1,000 m X 800 m was designated along the river. In this area, a system of parallel trails placed 100 m apart and marked at 100 m intervals was cut. In order to locate all the groups within this area, groups were repeatedly followed to their sleeping sites at dawn, and the locations of all the sleeping trees found were mapped. In the search of the groups both within and outside the census area, the authors were assisted by three experienced guides and by information on Aotus sleeping sites provided by local inhabitants.
Upon locating the current sleeping site of a group, which usually consisted of a hollow in a tree, the group was trapped during the daytime by plugging the entrance hole or holes, thus preventing the animals from leaving the roosting hollow. The group members were then handcaught and extracted from the hollow one by one. The groups that slept on branches or vinetangles were caught by isolating the sleeping tree from surrounding vegetation and then chasing the monkeys down to the ground, where they could be easily caught by hand.
After trapping these groups partially or completely, animals were transported using the procedures described for Callitrichidae and Cebidae by Encarnación et al [1977] and Encarnación and Tapia [1980]. Morphometric measurements included body weight, total length, and right upper canine length following Soini et al [1977]. Age was estimated based on canine length and wear, the presence or absence of Population Structure of Aotus nancymai / 3 permanent molars, and the state of overall dental wear. Estimation of age was also based on consideration of subcaudal and pectoral glands and genital pigmentation. The subcaudal gland is a triangular area situated on the ventral region of the base of the tail (with the apex directed caudally). This area produces an intensely odiferous, greasy grey secretion which sticks to the pelage. Its development is evident in both male and female juveniles. The pectoral gland is a concave triangular excrescence pointing caudally with rounded corners on the thoracic region. It occurs in both sexes but is well developed only in males, in which it is manifest from the postjuvenile stage. Light brown pigmentation of the external genitalia occurs in adults of both sexes. In males, pigmentation begins from the posterior part of the testicles, and in females from the posterolateral part of the vulva. Pigmentation of the external genitalia is most intense in adults although it also is observed in younger age classes.
