Procolobus Verus Research Articles

Association between olive colobus (Procolobus verus), Diana guenons (Cercopithecus diana), and other forest monkeys in Sierra Leone.

Close association between olive colobus (Procolous verus) and other monkeys (especially Cercopithecus species) has been observed throughout the range of P. verus in the forest zone of West Africa. To investigate the basis of this association, we made new observations in Sierra Leone, concentrated at 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. diana). 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 groups of olive colobus associated closely with a larger groups 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 secon Diana 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.

Interspecific associations of Diana monkeys, Cercopithecus diana, in Sierra Leone, West Africa: biological significance or chance?

The advantages of interspecific associations are invoked frequently without first testing the null hypotheses: (1) observed associations occur by chance, and (2) when associations do occur, the organism's behaviour is unaffected. During a study of two groups of Diana monkeys on Tiwai Island, Sierra Leone, the duration and frequency of interspecific associations were recorded along with behavioural and ecological data. Interspecific associations occurred in 36·6% of the samples from one group and 89·5% of the samples from the other. Predicted values of association based on null hypothesis 1 were generated using both Waser's gas model and computer simulation based on species density and group spread. For interspecific associations of Diana monkeys with the six other species of forest monkeys resident on Tiwai Island, only associations with olive colobus, Procolobus verus, could not be accounted for by random events (i.e. exceeded null model predictions). For both study groups, associations were non-random with respect to their range use. The frequency of different behavioural categories of Diana monkeys was not independent of association status, but both varied with time of day. No significant relationship between interspecific association and behaviour was found for either study group, when controlling for time of day. The effects of random processes must be considered before biological significance is attributed to interspecific associations.

The diet of the olive colobus monkey,Procolobus verus, in Sierra Leone

Observations of the feeding behavior of wild olive colobus monkeys (Procolobus verus)were made in southern Sierra Leone, West Africa. Most data came from systematically sampling one habituated social group, which inhabited old secondary rain forest on Tiwai Island. Olive colobus at Tiwai were highly selective feeders, obtaining most of their food from a small number of uncommon middle-canopy trees, from the forest understory, and from climbers. Mature leaf blades were largely ignored; young foliage (particularly of climbers) was a year-round dietary staple, while seeds, flowers, and mature leaf petioles were seasonally important. It is argued that this diet results largely from selection for two different attributes of food: high digestibility and physical location. Preferred foods had low fiber and tannin contents, while preferred feeding sites were in thick low growth and climber tangles. P. verusis the smallest extant primate species using a foregut fermentation system. Observations of its diet accord with inferences drawn from dental anatomy, digestive physiology, and considerations of body size.

La communauté de primates diurnes de la forêt de Taï, Côte-d’Ivoire

The community of diurnal primates living in the Taï Forest National Park, Western Ivory Coast is described. Besides the Chimpanzee, it includes four species of genus Cercopithecus (C. campbelli, C. diana, C. nictitans, C. petaurista), three species of Colobus (C. badius, C. polykomos, C. verus) and one Cercocebus (C. atys) Details are given on the relative abundance of the seven species found on a 2 km² study area which was closely studied from 1977 to 1983, together with their population density, age and sex ratios, and sizes of home-ranges. The ecological niche of every species is defined, based upon three major parameters : diet, vertical stratification within the forest structure, and the usual supports for locomotion. The Taï forest Cercopithecids are more often observed in polyspecific groups than in monospecific groups. However, all the species do not display the same tendency to associate with the others. It is the Olive Colobus Colobus verus which lives the more often in mixed groups (in 92 per cent of the cases !). It also associates preferentially with the three sympatric species of Cercopithecus, rather than with the other Colobines. The polyspecific troops of Cercopithecids of the Taï Forest can include as many as 6 different species of monkeys. Adaptive relationships between abundance and distribution of food resources, on the one hand, and group size, home range size, and strength of territorial behaviour on the other hand, are stressed. Scarse and patchy food resources favour large multimale groups exploiting large undefended ranges. Conversely, abundant and evenly distributed resources favors small unimale groups living on permanent territories. Information is given in an appendix on some behavioural idiosyncrasies of the Olive Colobus.

In Search of Rare Forest Primates in Nigeria

When the author visited Nigeria in 1981 to look at forests on the lower Niger, there had been no reports for 15 years of the red-bellied guenon Cercopithecus erythrogaster, and only a single specimen of the olive colobus Procolobus verus was known from the country. He found surviving populations of both monkeys, but each is threatened by widespread, intensive hunting, and by habitat destruction. If effective measures are not taken to protect the guenon and its rainforest habitat, this species could become extinct, since it occurs only in southwestern Nigeria.

Metric variability of the postcanine dentition in colobus monkeys.

AbstractThe postcanine dentition of three species of colobus monkeys (Colobus polykomos polykomos, Procolobus badius badius and Procolobus verus) is compared metrically for three characters: interdental relations, sexual dimorphism and interspecific relations. Interdental relations reveal that the postcanine teeth represent a single morphogenetic field, which supports Butler's concept on the nature of the differentiation and variability of mammalian dentition. However, comparisons of the coefficients of variation show that interdental differences are not significant, except in a few cases. Also, sex differences in variability are not significant. However, comparisons of the means reveal highly significant sex differences, particularly in the dimensions of the first lower premolar in all three species. The analysis of interspecific relations of the postcanine dentition supports the current idea about the systematics of colobus monkeys. The findings are discussed with comparative data from other cercopithecoids and hominoids.

OBSERVATIONS ON THE NATURAL HISTORY OF THE OLIVE COLOBUS MONKEY, PROCOLOBUS VERUS (van BENEDEN)

Summary. The Olive Colobus is a unique African member of the Colobidae, in that it is dull in colour, the sexes are equal in size, and it is monotypic over a wide range. It is a leaf‐eater in low levels of the stratified High Forest zone of West Africa, showing a marked tendency to feed, move and sleep in dense foliage. Consequently, it is, though fairly common, difficult to observe. Troops are small, and leadership by a dominant male, common in other species, is not observable. There is a marked tendency to aggregate at feeding‐places with other species of different dietary habits. This appears to be a protective habit. The young infant is carried in the mouth, an unusual habit among monkeys. It is possible that many of the characteristics of the Olive Colobus, and some of those of the Red Colobus, may be explained by an abnormal hormone balance, involving high concentrations of oestrogens.