THE BEHAVIOURAL ECOLOGY OF BALE MONKEYS (Chlorocebus djamdjamensis) IN THE DISTURBED ENVIRONMENT OF HARENNA BAMBOO FOREST, ETHIOPIA

Abstract

This study aimed to understand the behavior and ecology of Bale monkey in disturbed environment of bamboo forest. The study site was located in the southern escarpment of Bale Mountains National Park, specifically known as Rira locality. A focal animal sampling method was used based on a 10-minute observation period across the seasons. Data were collected on social system with associated behavioral and ecological components from 1973 focal animals watched, which included the deployment of a total group count to determine group size. The minimum convex polygon method was used to elucidate the effects of attractive food availability on the home range size of the group. Data were analyzed using a Generalised Linear Model (GLM). This study revealed that Bale monkey has a large group size in fragmented forest, which might be linked to the availability of attractive crops that further facilitated boundary overlap among the neighboring groups. Bale monkey group lives in a multi-male-multi-female social system. The group size was variable in every count, possibly due to the surrounding environmental conditions. Relatively larger group size recorded in wet season than in dry season (84 v 74, P<0.001). With the social partner, adult females were more associated with other adult females, juveniles and infants, whereas adult males did mainly with adult females. The group showed larger home range size in wet season (753.2 ha) than in dry season (27.8ha). Likewise, its daily travel length in wet season (6205m.) was significantly further than in dry season (1301m), p=0.032. This leads to evidence that Bale monkey group exhibits larger home range area and longer day range in disturbed forest than its published reports in undisturbed forest. Bale monkey exhibited a semiterrestrial behaviour (50.4% on trees and 49.6% on ground) unlike most forest - living guenons. This suggests that the temporal and spatial availability of attractive food sources and forest fragments significantly influence the substrate use of the Bale monkey. Arundinaria (bamboo plant) was the most frequently used substrate by Bale monkey across seasons. Plant species selected as food sources indicated that the bulk of the diet largely comprised of arundinaria, barley and grass species. Seasonal differences significantly influenced the proportion of the food items selected by Bale monkeys (p = 0.01561). In wet season, young Arundinaria leaf and shoot was the most preferred food items (p < 0.001), while barley is the most attractive food items in dry season. Bale monkey spent more time feeding but less so in dry season (51%) than in wet season (64%), P<0.001. The group spent more time resting in dry season (P<0.001), which might be influenced by the availability of cultivated food items. The proportion of activity patterns varied with time of the day. Resting and grooming were more pronounced around noon (P<0.001), while feeding largely took place around the mooring and evening. This study generally concluded that habitat fragments, availability of cultivated crop and other attractive food items and seasonal variability significantly influence the behaviors and ecological adoptions of Bale monkeys