Population Estimate and Behavioural Ecology of Omo River Guereza (Colobus Guereza Guereza) From Wof-Washa Natural and Plantation Forest, Central Highland Ethiopia

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Addis Ababa University


Population estimate and behavioural ecology of Omo River guereza (Colobus guereza guereza) from Wof-Washa Natural and plantation forest, central highland Ethiopia Dereje Yazezew Mammo, PhD Thesis, Addis Ababa University February 2019 Omo River guereza (Colobus guereza guereza) is a subspecies of eastern black and white colobus monkeys endemic to the western Rift Valley forests of Ethiopia. No detailed published information is available on this subspecies and it remains one of the least studied primates in Africa. With the current increasing habitat loss and degradation across its geographic range, data on the current conservation status and behavioural ecology are essential to design a management plan. This study therefore aims to provide data on the population estimate and behavioural ecology of Omo River guereza. Vegetation surveys were conducted within each group’s home range to quantify the overall vegetation composition. A total of 2 with 400-500 m long and 10 m wide vegetation transects were laid out and sampled the diversity of big trees ≥ 10 cm diameter at breast height (DBH= 1.3 m above ground). Phenological data were analyzed from 13 plant species: 10 trees, two shrubs and one climber. A total of 39 censuses from 1.5 to 3 km transects were conducted with a cumulative distance of 88.5 km in four different habitat types. The activity budget, feeding ecology and ranging behaviour were studied in two neighbouring groups for five minutes with 15 minutes interval scan sampling for 12 month study period. Plant species with DBH ≥ 10 cm in the range of natural forest group (N) had higher stem density (780 stems/ha) than plantation group’s (P) (600 stems/ha). Plant species diversity and evenness were higher and dominance was lower in the natural forest (N) than in plantation forest (P). Young and mature leaves were the most abundant plant parts throughout the year while fruit was the least abundant. There were statistical differences in food availability indices of young leaves (Mann Whitney U; Z=-4.16, P<0.001) and mature leaves (Mann Whitney U; Z =-4.15, P<0.001) between the two guereza groups across months. Out of the total 140 Omo River guereza groups sighted, the highest encounter rate was recorded in the undisturbed natural forest (3.11 groups/km) transect while the lowest were in the Erica- Juniperus mixed forest and disturbed natural forest. The total population estimate of the study species was 2947 individuals. Out of the average individual number (317) of Omo River guereza sighted during the three-census period, 56.3±17.1 (71%) were adult and 17.3 ±5.6 (21.8%) were subadult of both sexes. Guerezas spent 43.1% of their time resting, 31.8% feeding 12.9% moving, 5.1% grooming and 4.8% performing other activities. Guerezas were observed feeding on 31 plant species belonging to 26 families. Overall, guerezas diet constituted 56.44% young leaves, 26.59% mature leaves, 10.8% fruits and 6.17% was from other food items. The top five species from five different families comprised 83% (group P) and 70% (group N) of Omo River guereza diet of which leaves of Maesa lanceolata contributed 23.2% of the overall diet. Kernel density estimate revealed that group P shared 19.1% of its home range with group N while group N shared 10.6% of its home range with group P. Further study should be carried out to work out a proper management plan and minimize human interference.



Activity Budget, Feeding Ecology, Habitat Use, Population Estimate, WWNSF