Vertical bipedal locomotion in wild bearded capuchin monkeys (Sapajus libidinosus).

When carrying objects, nonhuman primates often show bipedal locomotion. Studies of primate bipedality, however, in both nature and captivity, have concentrated on locomotion on horizontal substrates, either terrestrially or arboreally. No observational or experimental study seems to have looked at non-horizontal bipedality, yet we show here that it occurs often in nature in Sapajus libidinosus, the bearded capuchin monkey. The context is transport of small food items from source to site of consumption, in which the monkeys usually carry handfuls of maize kernels over several meters' distance, both on the ground and in the trees. Most impressively, over a fifth of such bouts are done vertically, when the tree trunk is fully upright. Such vertical bipedality, with or without transport, apparently has not been reported before.

Ranging behavior of Mahale chimpanzees: a 16 year study.

We have analyzed the ranging patterns of the Mimikire group (M group) of chimpanzees in the Mahale Mountains National Park, Tanzania. During 16 years, the chimpanzees moved over a total area of 25.2 or 27.4 km(2), as estimated by the grid-cell or minimum convex polygon (MCP) methods, respectively. Annually, the M group used an average of 18.4 km(2), or approximately 70 %, of the total home-range area. The chimpanzees had used 80 % of their total home range after 5 years and 95 % after 11 years. M group chimpanzees were observed more than half of the time in areas that composed only 15 % of their total home range. Thus, they typically moved over limited areas, visiting other parts of their range only occasionally. On average, the chimpanzees used 7.6 km(2) (in MCP) per month. Mean monthly range size was smallest at the end of the rainy season and largest at the end of the dry season, but there was much variability from year to year. The chimpanzees used many of the same areas every year when Saba comorensis fruits were abundant between August and January. In contrast, the chimpanzees used several different areas of their range in June. Here range overlap between years was relatively small. Over the 16 years of the study we found that the M group reduced their use of the northern part of their range and increased their frequency of visits to the eastern mountainous side of their home range. Changes in home-range size correlated positively with the number of adult females but not with the number of adult males. This finding does not support a prediction of the male-defended territory model proposed for some East African chimpanzee unit-groups.

Case report of helminths and lung mite infection in the red-tailed monkey, Cercopithecus ascanius schmidti, in Mahale Mountains National Park, Tanzania.

We documented the presence of gastrointestinal nematodes and lung mites in two red-tailed monkeys, Cercopithecus ascanius schmidti, in Mahale Mountains National Park, Tanzania. We detected lung mites, Pneumonyssus duttoni, in the trachea and bronchioles, and five species of nematodes, Oesophagostomum pachycephalum, Ternidens deminutus, Streptopharagus pigmentatus, Primasubulura distans, and Trichuris sp. in their gastrointestinal tracts. This is the first report of a parasitological survey for the red-tailed monkey in Mahale Mountains National Park, and O. pachycephalum, T. deminutus, and P. distans were found for the first time in the red-tailed monkey.

Pirouettes: the rotational play of wild chimpanzees.

A pirouette is a locomotor-rotational movement in which a young chimpanzee spins around in a (mostly) quadruped posture while advancing forward in a straight line. We addressed whether this behavior evolved as a practice of general athletic ability or of sexual selection. The former hypothesis would predict no sex differences in skill or the developmental process, while the latter would predict the opposite. Chimpanzees most likely master the pirouette around the time of weaning. We found no conspicuous sex differences in the developmental process or the number of rotations per bout of pirouettes, so the pirouette's main function may be to facilitate general athletic ability. Infants pirouetted regardless of the context of rest or travel, whereas juveniles and adolescents pirouetted primarily during travel. This is consistent with the survival strategy hypothesis, because juveniles and adolescents would be expected to display pirouettes to many watchers if this practice were sexually selected. However, the fact that males tend to pirouette faster than females and to pirouette even during adolescence suggests that sexual selection has some influence in shaping the evolution of the practice. Despite this, no conspicuous tendency was found for juveniles or adolescent chimpanzees to display pirouettes to opposite-sex individuals. More data on adolescent individuals are needed to definitively determine the role of sex differences in pirouetting behavior.