RESULTS AND DISCUSSION

Population Density

The population density of Aotus at Rio Tahuayo was estimated on the basis of the total number of groups found existing in the 0.8 km 2 sample area at Huaisi. This area included two lots that had been cleared for cultivation and that measured 0.5 ha each. The Aotus density was found to be 8.75 groups/km 2 or 25 individuals/ km 2. On Isla Iquitos, an island of 53 km2, Soini & Moya [1976], using the transect method, estimated densities of 10 groups/km 2 . By means of nocturnal observations and, at daytime, location of troops at their sleeping sites, 9 groups/km 2 were esti mated for the same area [Soini & Moya, 1976].

During this study, it was observed that not all troops used tree hollows as sleeping sites and that some troops used up to five different sleeping sites. Thus, the number of known Aotus sleeping hollows in a given area did not necessarily reflect the total number of groups present, a fact that must be taken into account when estimating population densities on the basis of information on sleeping hollows.

Group Size

The sizes of the 42 groups varied from two to five individuals, with an average of 3.4 individuals per group (Table 1). Most frequently observed were groups of four individuals (19 groups or 45% of the total), while the least frequently observed group size was five (2 groups, 5%). Observations on Aotus , made by Hershkovitz [19831, Izawa [1976], Green [1978], and Heltne [1977] in Colombia and by Wright [1978, 1981] in Peru, were similar to our findings for A. nancymai. However, one of us (F.E.) observed groups of six individuals at Huaisi (Rio Tahuayo) and Nazareth (Rio Amazonas).

TABLE I. Summary of the Group Sizes of Aotus nancymai Trapped and Observed on the Rio Tahuayo Group.

Age Categories

Using the criteria described in the methods section, we defined five general categories with corresponding body weight, total length, and canine length (Table II).

TABLE II. Average Body Weight and Total Length in Free Ranging Aotus nancymai.

The size and weight ranges for adults (A) were 530 774 min and 550 950 g, respectively. Adult teeth were generally worn and stained with tartar. In some individuals, incisors were missing and canines were blunt or flattened. The subcau dal gland was well developed in both sexes, and the external genitalia were intensely pigmented. The males had prominent pectoral glands. The females' mammary glands were distended and lacked hair, had turgid protuberant nipples and milk in some cases. Males were heavier and longer than females, but these differences were not statistically significant (Table III) except for the canine length (Table IV).

TABLE III. Average Body Weight and Total Length in Free Ranging Aotus nancymai.

TABLE IV. Average Right Upper Canine Length* in Free Ranging Aotus nancymai.

*The distance from the edge of gingiva to the tip of the canine. Population Structure of Aotus nancymai / 5

The size and weight ranges for the subadults (SA) were 574 651 mm and 425 825 g. Subadult dentition was normal and complete. The canines did not have any wear and were sharp pointed. The subcaudal gland was little developed. The exter nal genitalia were only partially pigmented, but the male pectoral gland was developed and somewhat prominent. The female mammary glands were covered with hair and had small nipples. Males were significantly heavier and longer than females and had longer canines (Tables III, IV)

Juvenile (J) size and weight ranges were 490 609 mm and 450 575 g. Dentition was incomplete in most cases with either permanent or deciduous canines and the third molar absent. The external genitalia were lightly pigmented, and the subcau dal and pectoral glands were not yet fully developed. Females were heavier than the males but shorter. These differences, including those in canine length, were not statistically significant (Tables III, IV). However, the sample size for females was very small.

Infant 2 (I2) size and weight ranged from 413 to 524 mm and from 200 to 375 g, respectively. Dentition was incomplete and deciduous, with the first molar erupting in some cases. The external genitalia were generally unpigmented, and the subcau dal gland was absent. Females weighed more and were longer than males, but the differences, including those in canine length, were not statistically significant (Ta bles 111, IV).

Infant 1 (I1) size and weight ranges were 298 525 min and 100 200 g, respec tively. They were incapable of independent locomotion. Dentition was deciduous with no molars. The external genitalia were unpigmented, and the testicles were undescended in males. Females weighed more and were longer than males, but the differences, including those in canine length, were not statistically significant (Ta bles III, IV).

Social Organization

The basic composition of an Aotus nancymai group was that of a reproductive pair with progeny from one to three previous birth seasons (Table V). Only one of 14 captured groups had more than one adult male. One group was observed to contain three adults. The third adult maintained a distance of 2030 in from the rest of the group. An attempt, by this adult, to approach the group resulted in a fight that ended when both animals fell in the river and the interloper fled. When this group was captured later that day, the adult male was found to have recent slash wounds on one arm and on the pinna of one ear. The sex of the other combatant is not known, but it could have been a subadult male who was being forced to leave his natal group.

TABLE V. Composition of 14 Groups in FreeRanging Aotus nancymai That Were Completely Observed and Trapped*.

*A = adult; SA = subadult; J juvenile; I2 = Infant; I1 Infant 1. 6 / Aquino and Encarnación

On only one occasion was a solitary individual observed. This was after the capture of an entire group some days earlier. The solitary animal was captured and proved to be a female. She was probably a member of the captured group and had escaped our attention earlier.

The observed and captured groups of Aotus nancymai monkeys occupied a stable and defined territory which they defended by means of subcaudal scent marking and vocalizations. However, some partial overlap of territories is apparently common in Aotus [Wright, 1978, 1981]. In June, one of the authors (R.A.) observed a vocal confrontation lasting for 23 minutes, during which the groups maintained a distance of about 30m.

Population Structure

Results for the population structure were based on examination of 100 individuals, 14 groups from which all the individuals were captured and 23 groups that were only partially captured (Tables VI, VII). Sex ratio for groups that were completely captured was 1:1 for all ages except juveniles. We consider the juvenile sex ratio to be due to small sample variation (Table VI). The sex ratio for the total captured groups favored males for all age classes except infants for which the ratio was 1:1 (Table VII). However, this variant sex ratio can be explained by the fact that the females were more likely to escape during trapping.

Of the five age categories, juveniles represented only 6% and 7% of the total populations in each case (Tables VI, VII). This age may be the most critical one for individual survival as juveniles are without paternal protection since the male devotes his attention to the care and protection of the infant.

TABLE VI. Population Structure of the 14 Groups in Free Ranging Aotus nancymai That Were Completely Trapped Ages.

TABLE V11. Population Structure of the 37 Groups in Free Ranging Aotus nancymai That Were Completely and Incompletely Trapped Ages.