To explore sources of variation in tropical forest primate biomass, and, in particular, to test the hypothesis that soil conditions are a major ultimate determinant of the biomass of colobine monkeys and other primates, we compared data on the soils, vegetation, and primate community at a site in West Africa (Tiwai Island, Sierra Leone) with information from other sites, especially two other African sites (Douala—Edea in Cameroon, and Kibale Forest in Uganda). The biomass of eight anthropoid primate species in old secondary high forest on Tiwai was estimated from data on population densities assessed by transect samples combined with data on social group densities and individual body masses. Samples of soil and tree foliage were collected at the same site, and subjected to a variety of chemical and mechanical analyses. Our estimate of anthropoid biomass at Tiwai is 1229—1529 kg/km2, including 682—889 kg/km2 of colobines. This is one of the highest primate biomasses recorded anywhere. The soils at Tiwai were found to be relatively high in sand content and low in pH, and to have low levels of mineral nutrients. Levels of condensed tannins in the mature foliage of the trees comprising a major part of the forest canopy were higher than at other sites, but the ratio of protein to fiber in this foliage was also higher than at any other site except Kibale. It is argued that a wide range of environmental factors affect primate population densities, and that nutrient—poor soils and high tannin levels in tree foliage do not necessarily produce a low primate (or colobine) biomass, as some earlier studies had suggested. Furthermore, seeds (an important food source for Tiwai colobines) are apparently a common part of the colobine dietary repertoire and are not consumed largely as a response to a scarcity of digestible foliage.

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We provide the first documented case of the extinction in the twentieth century of a widely recognized primate taxon. During surveys in Ghana and Côte d'Ivoire in 1993–1999, we were unable to find any surviving populations of Miss Waldron's red colobus monkey (  Procolobus badius waldroni), a primate taxon endemic to the forests of this part of West Africa. We conclude that this monkey, which at least one authority considers worthy of species status, is probably extinct. Hunting by humans appears to be the ultimate cause of the extinction. Until our surveys began, little attention had been paid to the plight of this red colobus monkey, despite its listing as endangered by the World Conservation Union. The extinction of other large animals in the Upper Guinea rainforest region is likely to follow soon unless more attention is paid to the full range of endangered forms and more resources are devoted to their rigorous protection.

Close association between olive colobus (Procolobus uerus) and other monkeys (especially Cercopithecus species) has been observed throughout the range of P. uerus in the forest zone of West Africa. To investigate the basis of this association, we made new observations in Sierra Leone, concentrated a t Tiwai Island. We obtained data on the association patterns of monkeys over a large area of the island from line-transect samples, and studied association behavior via long-term observational sampling of habituated groups of olive colobus and Diana monkeys (C. dmna). During transect sampling, olive colobus always were seen less than 50 m from monkeys of other species, especially Cercopithecus. In studies of habituated groups, we found that one group of olive colobus associated closely with a larger group of Diana monkeys for more than 3 years. Members of the two groups were within 50 m of each other on over 80% of scan samples; the two groups shared the same range, but foraged in different parts of the canopy and had little dietary overlap; association was maintained by the behavior of the colobus. The olive colobus was the only Tiwai monkey species seen less than 50 m from members of a second Dlana study group more frequently than expected, although in this case the two species were associated during less than 12% of samples. In both cases, we detected month-to-month variation in association frequency. We suggest that olive colobus has a strong tendency to associate with other monkeys as part of an evolved strategy; that observed association patterns depend on the ranging habits and group dispersion patterns of the other species in the area; and that this strategy evolved because it reduces predation risk for a small-bodied monkey that forages in small, dispersed groups.

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ABSTRACT. I report an incidence of chimpanzee (Pan troglodytes verus) cracking of Detarium senegalense (Caesalpiniaceae) At 16:35 chimps were observed leaving the area. The group included two adult females (one with a moderate sexual swelling, ca. 7 cm), one subadult or adult female, one medium size juvenile of indeterminate sex, and two large infants or small juveniles of indeterminate sex (one of these was carried piggyback by an adult female).Upon close investigation of the location at which the chimps were first detected, I found numerous (ca. 100) freshly opened pods of Detarium senegalense (Caesalpiniaceae) scattered in an area about 10 m in diameter. This area was directly beneath the crown of a largeDetarium. The majority of the freshly opened pods were clustered around three large, broad surface roots which were freshly scarred.Detarium senegalense trees are not uncommon (about 0.15 individuals per hectare within the two main study areas on Tiwai Island) but are wid.ely scattered as individual trees throughout the forest. The fruits are composed of a single seeded disc-shaped pod 5 to 6 cm in diameter and I to 1.5 cm thick. The pod wall is extremely hard (ca. 2 mm thick); I could 1) Tiwai Island (7~ ll~ is a large (ca. 10 km 2) river island in the Moa river in southwestern Sierra Leone. open pods only with the aid of a hammer. The seed is large (ca. 5 • 1 cm) artd, like the pod, disc-shaped. When mature, the pod wall is covered with a thick fibrous pulp making the entire fruit ca. 5 to 6 cm long and ca. 4 cm thick. After the fruit drops from the tree, the pulp decays in two to four months leaving only the pod wall and its contained seed. Fruits on the ground for several months with little or no pulp remaining appear to be those selected by chimps for cracking.The nuts opened by chimps are characterized by being broken transversely across the disc (Fig. 1). Bush pigs (Potamochoerus porcus) also occasionally eat Detarium seeds, but they apparently open the nuts with their teeth by splitting the pods laterally along the suture line.Because the chimps were not observed opening the nuts, their cracking method is not known. However, when the chimps were observed leaving the area, they were not carrying stones. I found no stones in the immediate area that may have been used for nut cracking. Three other methods seem plausible: (1) placing the nut on a surface root anvil and striking it with a stick; (2) same method as above, but using a second Detarium nut in lieu of a stick; and (3) holding the nut to be cracked in the hand, and then striking it directly on the surface root anvil. Of these, the third seems least likely due to both the hardness of the nuts and the volume of noise produced (cracking a nut by holding it in the hand would tend to muffle the noise). BozscH and BOESCH (1983) observed chimps in the Ivory Coast open fruits of Strychnos aculeata (Loganiaceae) by holding them in the hartd and banging them against a hard surface, but they only report tool use for cracking Detarium nuts.The most likely...