Activity patterns, habitat use and mortality risks of mangabey males living outside social groups

Isolated individuals of most species are thought to be at a higher risk of mortality from starvation and predation than those in groups. However, supporting evidence remains scant. As part of a broader study of grey-cheeked mangabey, Lophocebus albigena, dispersal in Kibale National Park, Uganda between October 1996 to February 1999, we investigated starvation and mortality risks within a sample of 27 radiotagged mangabey males. Each male was contacted on average three times a week to collect data on spatial relations, habitat use, activity patterns and fates. We assessed risks by comparing data from 'isolated' (greater than or equal to 200 m from the group) males with data from 'within-group' males. We assessed starvation risks by comparing proportions of time spent in feeding, foraging and moving, comparing rates of movement during focal samples, and comparing proportions of time that males spent in different habitat types and canopy levels. We assessed mortality risks by comparing scanning rates and mortality events of within-group and isolated males. Isolated males spent significantly more time scanning, but we could detect no other significant differences in time allocated to different activities by the two categories of males. Nor could we detect differences between within-group and isolated males in the use of habitat types and canopy levels. At least three of five established mortality events involved males known to be isolated from groups. Given that males were found isolated only 11% of the time, it is estimated that isolated males were at least 12 times as likely to die as within-group males. These results suggest that dispersing males may not face increased risk of starvation, but are at higher risk of mortality (primarily through predation by eagles) than nondispersing males. (C) 2001 The Association for the Study of Animal Behaviour.