Social organization in the mountain nyala (Tragelaphus buxtoni) population in the Bale Mountains National Park, Ethiopia

Abstract

This study was conducted in 2009 and 2011 in the Bale Mountains National Park in Ethiopia to assess social organization of endemic and endangered mountain nyala. The main objectives of this study were to identify social group types of the mountain nyala in the park, and to determine the frequency of occurrences, group sizes and number of age/sex categories in social group types. Based on age/sex composition, five social group types were distinguished: all-male, all-female, male-female, female-juvenile and male-female-juvenile group types. A total of 572 groups and 5187 individuals of mountain nyalas were recorded during the study period. Overall mean and typical group sizes for the species were 9.1 ± 0.5 (range: 1–107) and 24 animals, respectively. Male-female-juvenile social group type was the most frequently observed group type (31% of the total records), contained the highest proportion of animals recorded (64%) and had the largest mean group size (18.5 ± 0.8) and typical group size (31.9) than the other social group types. Lone animals constituted 16.3 and ~2% of the total groups and animals recorded, respectively, in which over two-thirds of them were adult males. Both mean number and proportion of individuals of each age/sex category across social group types significantly increased when they were associated with one or two other age/sex categories than when not associated. In general, data presented here represents the first detailed information available on the species’ social organization behaviour and provides important base-line information.   Key words: Group size, mountain nyala, park, social group, social organization.