A troop of olive baboons, Papio anubis, was studied for 11 months in an open-country habitat near Gilgil, Kenya. Detailed mapping of troop movements was undertaken and provided a precise picture of range usage, showing that a small part of the range was used intensively. Gradations of home range use are described quantitatively. Tendencies to spread out and coalesce in different parts of the range are investigated. Shifting ranging patterns are examined together with meteorological factors, seasonal food supplies and water availability.

Most cercopithecines reproduce on a seasonal basis, but the proximate mechanisms influencing birth periodicity are often unclear. We analyze 10 years of data from the Gilgil Baboon Project (Kenya) in order to examine the relationship between annual birth patterns and rainfall. Savanna baboons at Gilgil copulated in all months of the year, and births did not occur on a seasonal basis. Annual rainfall patterns showed no association with annual birth patterns, but the chances of conception were significantly greater following the end of the long rainy season than at other times of the year. Nonseasonal reproduction is a general characteristic of savanna baboons (Pαpio cynocephalus subsp.) throughout Africa. The extreme dietary diversity of baboons enables them to utilize a wide variety of resources and facultatively manipulate the timing of different stages in the reproductive cycle in accordance with resource availability. We predict that nonseasonality of reproduction will be more likely to occur among species with a large dietary diversity than among species with a more restricted diet.

An habituated group of wild patas monkeys was observed in Kenya for 550 h in 1984. Observations were made primarily during an interval that, as previous studies at the same site had demonstrated, coincided with the annual mating and conception periods. Earlier field studies of patas at other sites had reported that heterosexual patas groups had only a single resident adult male and that mating was harem-polygynous. At the Kenya site, by contrast, as many as six males were simultaneously resident and mated in the group during the conception period. Males adopted a variety of tactics to gain access to receptive females, ranging from opportunistic mating to attempts at sequestration that resembled consort behavior in other cercopithecoids such as savanna baboons and rhesus macaques. Aggressive competition for access to females took place among the males, although the number of completed copulations per male did not bear a positive relation to agonistic dominance rank. For patas monkeys, harem polygyny is only one available option within an overall mating system that is best described as a form of promiscuous polygyny, especially during periods when conception is most likely.

During 1970During -1971, a troop of 49 olive baboons was observed in a partially protected area in Kenya, not far from the village of Gilgil. The baboons were seen to catch and eat 47 small animals, a rate of predation far higher than has been reported for any other nonhuman primate. Prey animals included hares, small antelope and the neonatal young of larger antelope. Adult male baboons caught and ate all but three of the prey animals. Adult females caught hares three times, but only once was a female able to keep and eat most of the animal she had caught. There was n o significant seasonal variation in the occurrence of this behavior. The baboons appeared to search out prey deliberately and to come upon it by accident. No instances of cooperative hunting or voluntary sharing were seen, Both incidence and form of this predatory behavior may be influenced by learned, local tradition.

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