Behavioural Indicators of Stress
The impact of social structure on self-directed behaviour.
Self-directed behaviours, including scratching, auto-grooming, body shaking, and yawning, have all been shown to reflect some level of stress, anxiety, or uncertainty in baboons and macaques (Maestripieri et al 1992; Castles & Whiten 1998). In long-tailed macaques, scratching and autogrooming are more frequent when an individual is within one meter of the alpha male than when alone or in passive contact (Pavani et al 1991; Troisi & Schino 1987). Troisi and Schino (1987) suggest that this can be explained as an internal conflict between two opposing social motivations: the motivation to approach the alpha male and groom him and the motivation to avoid him in case he attacks. Among female olive baboons, a behavioural index reflecting a combined measure of scratching, autogrooming, self-touching, body shaking, and yawning was forty percent higher when the female's nearest neighbor was higher-ranking than when it was lower-ranking than herself (Castles et al 1999).
In this study we are measuring the occurrence of self-directed behaviours in the ‘Cape Point’ troop of chacma baboons. This troop inhabits the Cape of Good Hope section of the Table Mountain National Park in the Cape Peninsula of South Africa. The aims of the study are to quantify SDB rates in the study troop, compare them to other available data on female baboons, and investigate the relationship between SDB rates and (a) female dominance rank, (b) reproductive state, and (c) herding by baboon monitors. The study troop is unusual in two ways: (1) it lacks adult males and (2) it is regularly herded away from tourist areas by park staff employed as baboon monitors (see ‘Baboons and Humans’ sidebar on the BRU home page). Fifteen-minute continuous focal samples are being conducted on females, in which the occurrence of SDBs (scratching, self-grooming, yawning, and body-shaking) is recorded. We expect the unusual social structure of this troop to have an effect on their SDB rates. In particular, the absence of adult males in the troop and the consequent lower average rank of a female's nearest neighbor should result in lower overall rates of self-directed behaviour compared to a chacma troop with adult males. Certain categories of females, however, might be expected to engage in higher rates of self-directed behaviour, e.g., females with young infants (who stand to lose when a new male immigrates into the troop) and estrous females (who are in a state of sexual arousal). Results of this study promise to have implications for both baboon social behaviour and management of this population.
