Social Organisation, Ecology and Reproduction in the Sanje Mangabey (Cercocebus Sanjei) in the Udzungwa Mountains National Park, Tanzania

Abstract

<p>Understanding of the biology of threatened species is central to effective planning for sustainable management of wildlife. The Sanje mangabey, Cercocebus sanjei of Udzungwa Mountains National Park in Tanzania is under pressure from increasinghuman hunting, and habitat loss threatens its long-term survival. This thesis endeavoured to document the socio-biological and ecological aspects of this little-known species in a small habituated group of 62 individuals within the Mwanihana forest in Udzungwa Mountains National Park. I studied the social organisation, size and age-sex composition of one group by following and monitoring of the Sanje mangabeys over a six-month period. I also investigated the spatial-temporal interactions and associations between age and sex classes within a group. I assessed the Sanje mangabey's ranging and movementpatterns and monitored its reproductive behaviour by examining female sexual skin swellings and relationships between sexual swellings and sexual behaviour. Further, I investigated the species feeding habits and influences of seasonal parameters (rainfall and temperature) upon reproduction, feeding ecology and behaviour of this species. The Sanje mangabey social organisation is structured in a hierarchy characterised by dominance according to the sex and age of individuals. The study group was composed of individuals of all sexes and age classes; newborn babies, juveniles, sub adults and adults, males and females. Adult males were generally dominant overfemales and males of lower age. Males showed more agonistic behaviours to juveniles than did females and there were stable linear dominance hierarchies among individuals across the sexes (Landau's dominance index, h' =0.92, p =0.0281) and a high directional consistency index, DC =0.91) for both sexes. The linearity indices 'h' were 0.84, P= 0.041, DC = 0.94 and 0.93, P = 0.0382, DC = 0.94) for males and females, respectively. Individuals spent about 8% on average of day grooming each other and the rate of grooming differed across and within sexes and age classes. There was a significant relationship between duration of the initiator's first grooming episode and subsequent reciprocation by the receiver in all age classes (P < 0.05). The independent effects of total grooming duration of the initiator also showed a significant difference and predicted total grooming duration of the recipient (P =0.0001). However, there was no evidence for grooming to be directed towards higher ranking Sanje mangabeys. The Sanje mangabey's home range was 301 hectares and exhibited a mean daily range of 1760 metres within the Mwanihana forest. The rangeand movement patterns of this species differed significantly between seasons of the year. During the dry season (no rain) the group covered larger distances (P = 0.001) between forest patches and moved significantly faster (P = 0.001) than during wet (rain) season. The Sanje mangabey is omnivorous, feeding on plant material, invertebrates and vertebrates such as lizards. There were marked influences of temperature and rainfall on the feeding patterns. Mangabeys utilised the arboreal layer (>16m high) during cool and wet periods and were observed feeding mostly on the ground resources during hot and dry periods. The reproductive potential and social behaviour of theSanje mangabey, however, did not vary with the different seasons of the year. Sanje mangabeys have a mean swelling cycle length of 32.1 +/- 2.4 days. Individual females showed differences in swelling duration (F =12.43, P = 0.043) and noevidence of group variation in cycle length (H= 30.2, DF = 6, P < 0.05) was seen. Maximum swelling lasted for 4.4 +/- 0.9 days on average and detumescence was 14.7 +/- 3.9 days. The mean menses length was 3 +/- 0.2 days (n = 3). Most cycling females, showed days with regular swellings of both sizes. The gestation length averaged 173days and the interval between birth and resumption of the swelling cycle was observed to be 184 days. The sexual skin swellings appear to be sexually attractive signals of female reproductive condition. Although mating occurred in all stages of the female cycle, a peak was observed during maximum swelling size and breakdown. These findings illustrate the utility of sex swellings as signals used by males to determine reproductive condition.</p>