Patterns of foraging, ranging, and interspecific associations of Diana monkeys (Cercopithecus diana) in Sierra Leone, West Africa

Diana monkeys (Cercopithecus diana) are relatively large, highly arboreal guenons of the West African rain forest zone. I conducted the research reported here on two different study groups of Diana monkeys which occupied two different study areas located on Tiwai Island $(7\sp\circ 33\sp\prime$N, $11\sp\circ 21\sp\prime$W), a 12 km$\sp2$ island in the Moa River of southern Sierra Leone. I collected data on the ecology, behavior, and interspecific associations via scan sampling for each of these study groups during at least 12 consecutive months (July 1983-June 1984). In addition, I conducted 28 single-observer transect samples and 17 sweep samples to assess primate populations over the southern two-thirds of Tiwai Island.The vegetation type in both study areas was predominantly old secondary rain forest. All large trees ($\geq$20 m in height or $\geq$40 cm in diameter) contained within the two study areas were enumerated; sampling of smaller trees also was conducted. I collected data on the flowering, leafing, and fruiting patterns of 13 species of plants twice each month for the period reported here.One fully adult male and seven adult females resided in each of the study groups throughout the study; the two groups, however, contained different numbers of juvenile animals. The larger of the two study groups (Group E) occupied an annual home range of 28${1\over2}$ ha while the smaller study group (Group W) occupied an annual home range of 40${3\over4}$ ha. The mean day-range length for the two study groups was also different (Group W: 1019 $\pm$ 28.1 m/day (X $\pm$ S.E.), N = 72; Group E: 1532 $\pm$ 67.8 m/day (X $\pm$ S.E.), N = 36). In addition, the two study groups displayed marked differences in the patterning of activities and in the ways in which they used their home ranges. Although the study groups also displayed some differences in diet and in their patterns of food use, these differences were much smaller than those shown for activity and ranging patterns. Diana monkeys feed principally on fruit with arthropods, leaves, immature pod fluid, and flowers as important, and largely seasonal in the case of the last three categories, dietary supplements.The two study groups spent large proportions of time in association (within 50 m) with other species of non-human primates (Group W 36.6% and Group E 89.5% of time). Despite the large difference between the study groups in time spent in association, only association of both groups with olive colobus monkeys (Procolobus verus) could not be accounted for by random events (i.e., exceeded null model predictions)