Distribution of the Bale monkey (Chlorocebus djamdjamensis) in the Bale Mountains and its Ecology in the Odobullu Forest, Ethiopia – A Study of Habitat Preference, Population Size, Feeding Behaviour, Activity and Ranging Patterns

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Addis Ababa University


The Bale monkey (Chlorocebus djamdjamensis) is endemic to Ethiopia. Bale monkeys are recorded as Data Deficient in the IUCN Red List of Threatened species categories. This study was conducted from August 2007 to May 2008 to determine the habitat preference, population size, feeding ecology, activity and ranging patterns of the Bale monkey in the Odobullu Forest and distribution pattern across the Bale Mountains, Ethiopia. A total of 136 censuses of 1.8 to 3.2 km transects were conducted with a cumulative distance of 302.4 km in three different habitat types. A total of 62 Bale monkey groups were sighted and all of the encounters were observed in the bamboo forest habitat. In addition, the two study groups spent all group scan time exclusively in the bamboo forest habitat irrespective of seasons. Thus, Bale monkeys could be considered as bamboo forest specialists. The average group encounter rate of the monkeys in the bamboo forest was 0.44 per km and the average density was 124.69 per km2. The total population of Bale monkeys in the Odobullu bamboo forest is estimated to be 1746 individuals. The distribution of Bale monkeys in the Odobullu Forest was interlinked with bamboo forest habitat. The presence or absence of Bale monkeys in the bamboo forest habitat with altitude between 2400-3250 m asl was surveyed in the Bale Massif and three new Bale monkey populations were discovered. The activity pattern, feeding ecology and ranging behaviour were studied in two neighbouring groups with 15 minutes interval scan sampling for eight month study period. Feeding comprises the majority of their activity time with 65.7% followed by moving and resting that comprises 14.4% and 10.7%, respectively. Bale monkeys spent 7.1% of their time for social and the remaining 2.4% for other activities. The overall diet composition of Bale monkeys was dominated by young leaves, contributing 80.2%. In addition, they feed on fruits (9.6%), flowers (3.1%), animal preys (2.3%), shoots (1.5%), stems (1.4%), mature leaves (1.1%) and roots (0.9%). Bale monkeys consumed a total of 11 plant species, of these, the top five accounted 94.3% of their overall diet. Of these, bamboo (Arundinaria alpina) contributed 76.7% of their overall diet, of which 73% was from young leaves. The mean daily range length for the study groups was 928 m and the average yearly home range size of the study groups was 15.2 ha. The narrow ecological niche of the species may be a threat for its survival due to the bamboo harvest by local people for commercial purposes. The population status and distribution pattern of the Bale monkeys has to be studied in the neighbouring Bale Mountains Massif as well. Results from such future studies combined with these obtained in the present study could contribute in preparing proper management and conservation plans for the Bale monkeys. Thus, appropriate management action should be taken to conserve the species and their most important food resources, bamboo. Key words: Bale monkey, diet, distribution, Ethiopia, habitat preference, home range, Odobullu Forest, population size



Bale monkey, diet, distribution, Ethiopia, habitat preference, home range, Odobullu Forest, population size