Lloyd, P. H., & Rasa, O. A. E. (1989). Status, reproductive success and fitness in Cape mountain zebra (Equus zebra zebra). Behavioral Ecology and Sociobiology, 25(6), 411–420.
Abstract: Demographic data relating to herd size and stability are given for a population of Cape mountain zebra (Equus zebra zebra) under longterm observation. Temporal dispersion patterns of male and female offspring differed and were independent of the mother's status. Dispersion in females appeared to be related to physiological state, and dispersion in both sexes was related to age rather than changes in parental behaviour. Reproductive success of dominant and subordinate mares was equal and independent of age and social and reproductive variables. Fitness of dominant mares, however, was significantly higher than that of subordinates, the latter having a higher foal mortality, part of which could be attributable to dominants' aggression. The fitness of all males born was 1.6:1 compared with all females. Dominant mares produced significantly more daughters than sons. This trend was not found for subordinates. Mother's status was positively correlated with dominant status in her female offspring but not related to the subsequent status of her sons. Daughters had a more than twice as great a chance of breeding than sons. For maximum fitness gains, therefore, dominant mares should produce more daughters, since a high proportion of these would also have high status and fitness. This tendency is reflected in the sex ratio skewed towards females found for dominant mares.
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Rasa, O. A. E. (1998). To stay or to leave? Decision rules for partner species relocation in two symbiotic pairs of desert beetles. Anim. Cogn., 1(1), 47–54.
Abstract: Four nocturnal Kalahari desert tenebrionid beetles live in closely associated species pairs. The larger member of each pair, Parastizopus and Gonopus, are the primary burrowers while their smaller associates, Eremostibes and Herpiscius, inhabit the burrows with them and feed on detritus the larger beetles carry in. During summer drought, the two large species have different emergence times, surface activity patterns (vagilities) and different probabilities that burrows will be reoccupied before sunrise or remain empty for longer periods. Because their partners leave the burrows, the smaller species must make a decision either to stay in the expectation of a burrow being reinhabited, or leave and locate a new partner. The vagility and burrow fidelity of the associating species were studied using marked individuals in free-living populations. Field inclusion/exclusion experiments to test what influences the decision process showed that neither continual partner presence nor food induced the smaller beetles to remain. Different percentages, depending on species, left overnight. For both associates, these proportions corresponded exactly to the probability that the burrow would not be inhabited by their partner species the next day. Neither species predicted the probability of burrow reoccupation after a short vacancy and adopted a “waiting” strategy.
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Slabbert, J. M., & Rasa, O. A. E. (1997). Observational learning of an acquired maternal behaviour pattern by working dog pups: an alternative training method? Appl. Anim. Behav. Sci., 53(4), 309–316.
Abstract: German shepherd pups from untrained bitches and bitches trained in the location of narcotics were either separated from their mothers at 6 weeks (standard raised) or at 3 months of age (extended maternal care). Pups with extended maternal care which were allowed to observe their trained mothers locating and retrieving a sachet of odour-producing narcotic between the ages of 6 and 12 weeks performed the same task significantly better than non-exposed pups when tested at the age of 6 months, without further reinforcement during the interim period. This difference in performance was independent of the duration of maternal care or maternal origin of the pups and was attributed to differences in early experience acquired through observational learning.
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