Conservation status and determinants of Golden monkey (Cercopithecus mitis kandti) abundance in Mgahinga Gorilla National Park.

Abstract

Understanding the mechanisms permitting some species to thrive in disturbed or marginal habitats provides insight required to formulate informed conservation plans and requires knowledge of factors that influence abundance of the given species. Two broad approaches have been used to investigate such factors. One approach is to evaluate nutritional requirements of a given species and determine whether or not their habitat is providing its needs. Alternatively, if long-term data are available on changes in both population size and habitat structure, one can evaluate whether regeneration or degradation of the habitat corresponds with predictable changes in primate populations size. This study used the former approach to investigate dietary determinants of abundance of the golden monkey (Cercopithecus mitis kandti) in Mgahinga Gorilla National Park (MGNP), Uganda. The Virunga golden monkey population may be the only remaining viable population of golden monkeys. Golden monkey populations in other areas are disappearing through loss of habitat and interbreeding with related sub-species. The Virunga ranges have in the past, and are presently being degraded by human activity. In addition, the area is intrinsically depauperate of tree species that produce fruit for primates such as the golden monkey which is broadly characterized as a frugivore. This study was conducted using systematic instantaneous scan samples of feeding behaviour during day-long follows on one habituated group. Comparative data from Kibale were obtained from publications of authors who collected data on blue monkeys using a similar sampling procedure. Golden monkey foods were analyzed for levels of nutritional components and secondary compounds in the ten most frequently eaten foods. Phenological patterns were examined for 5 food tree species, three vines and two woody shrubs. Patterns of food plant distribution and habitat use were analyzed using a grid system of 0.25 ha cells set up in the study group’s home range. Golden monkeys fed on few plant species. Over the entire study only 5 plant species constituted 95% of golden monkey foraging effort, including bamboo at (59.9%), Maesa lanceolata (18.7%), Hypericum revolutum (6.8%), Galiniera coffeoides (2.1%), and Ilex mitis (1.4%). Maesa lanceolata fruited most in August (3.64 ± 3.34 SD mean phenophase score), September (3.14 ± 2.93 SD) and October (3.00 ± 2.86 SD). Hypericum revolutum flowers were most abundant during January (3.2 ± 1.62 SD), February (4.6 ± 2.01 SD), and March (2.33 ± 1.41 SD). Feeding effort on these items was highest during these respective periods and influenced ranging patterns. The study group used a total of 67.5 ha (272 cells) and an average of 15.3 ± 0.92 SE cells (CV = 21.87%) per month. It used an average day range of 15.32 ± 0.51 SE cells (CV 29.40%). The day path length averaged 898 m ± 32 SE (CV 29.78%). Diets of C.m.kandti and C.m.stuhlmanii, did not differ in terms of proteins, fibre, lipids and sugars or in avoidance or ingestion of secondary compounds. This study confirms previous suggestions that C. mitis has a very flexible dietary strategy, and cautions against evaluating habitat suitability based on the availability of the different food categories, particularly scarcity of fruit, and suggests that the nutritional value of potential foods be assessed. The golden monkey balanced their diet by obtaining protein from bamboo and sugars from the few fruits available or from flowers and leaf sources. Range use pattern generally followed food tree basal area distribution pattern. The abundance of three important food plants, Maesa lanceolata, bamboo and Hypericum revolutum, correlated with golden monkey range use over the entire study. Density estimates from censuses of golden monkeys conducted in the same area at different times indicated that initially there was an increase following improved protection and then a decline of the population over a 14-year period. Similarly, sighting rates show that there has been a continuous decline over the same period. While there were no differences in the nutritional quality of the diets of C.m. stuhlmanii and C.m. kandti, golden monkeys had a lower infant to adult female ratio than any other blue monkey subspecies for which data exist, suggesting that fewer infants are born into these groups probably due to greater nutritional stress. This study’s findings highlight the plight of the golden monkey whose population has continued to decline despite improved protection. It shows the need for conservation measures to protect golden monkeys as well as further exploration of other factors not examined under this study such as disease, along with studies in other parts of the golden monkey habitat range.