 Reference Base  Investigations on the social and reproductive behaviour o... |
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Meister, J., 1998. Investigations on the social and reproductive behaviour of captive White rhinoceroses (Ceratotherium simum simum). EEP Research Group Newsletter 5: 14-16
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| Location: |
World |
| Subject: |
Behaviour - Social Behaviour |
| Species: |
White Rhino |
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In zoos, aggression dependent on feeding method. In this Ph.D. thesis, captive White rhinoceroses observed for their social behaviour. Some animals were also studied when they were confronted with changing feeding situations, i.e. when food was offered on just one heap (clumped feeding) or in as many heaps as animals present (dispersed feeding). Clumped feeding is comparable to the common keeping routine in most zoos.
All animals were involved in aggressive interactions, both as actor and recipient. Since it was impossible to identify an -animal, towards which no aggressive acts were directed, ranking was done according to Coulon (1975). In all 5 groups the male was the aim of most aggressive behaviours. Since he retreated in most cases, his social position was low. The relationship of both genders is discussed in detail in the thesis, since females actually communicate formal subordination. The females that were regularly cycling or mated, or which were accompanied by a calf, were the top-ranking animals. The feeding experiments revealed that rhinoceroses were more aggressive when food was clumped, but just as under dispersed feeding conditions, most interactions were threat displays. These tendencies could be observed not only while the animals were feeding, but also during the rest of the day. An increase in aggression was also reported for White rhinos normally kept on a pasture, if they were fed with hay at just one feeding-site. Due to these changes in frequency, White rhinos seem to resemble ?scramble' feeding types. Scrambled species establish a more non-hierarchic, egalitarian social system. A feature of this social system is that the individual signals its current motivational status, eg. by an obvious willingness to 'fight', both in advance of and during a conflict situation.
In nearly all animals, the motivation to pass in a contest situation increased under clumped feeding conditions and decreases under dispersed feeding conditions. Feeding time decreased during clumped feeding. Walker (1997) could demonstrate that feeding time decreased if gras was offered to captive White rhinoceroses that were normally fed with hay. This observation points at the impact of competition on behaviour. The hypothesis of a motivational influence could be further proved in this study since the number of aggressive interactions decreased as a function of time in the clumped feeding situation. On the one hand, this may be the effect of a certain habituation when each animal has gained access to the feeding-site. On the other hand, the motivation to fight for food may decrease, since the animal become less hungry or the resource value decreases since there is less food left.
Since agonistic interactions proved to be stressful, free cortisol was analyzed by microtritreplate enzymimmunoassay (EIA). In contrast to the assumption, the urinary cortisol concentration of the male, as main recipient of aggressive acts, was not elevated. A significant difference could be found between the females that were the highest and the lowest ranking animals of this group. The number of sociopositive contacts in captive white rhino is small compared to the number of aggressive acts (3:1 - 6:1). ?Scramble' feeding type species do not need to form coalitions and alliances that are reinforced by numerous sociopositive contacts. Therefore, a change in feeding style should not cause a change in the frequency of sociopositive contacts. Against this prediction, the number of sociopositive contacts decreased under dispersed feeding conditions. Most of these interactions took place between bonded females (dyads or triads). This kind of relationship occurs both in the wild and in captivity. In the present study bonded females ?assisted' their partners in agonistic interactions especially with the male. No advantage of being with one's bonding partner could be observed as far as access to the feeding-site was concerned. Nevertheless, the triads and dyads respectively, avoided each other when several feeding sites were available and they fed frontal to each other in the clumped feeding situation. Bonded females preferred to feed side to side.
Since the number of sociopositive interactions grew concurrently with the number of aggressive acts, these interactions could act as reinforcement of the specific bondage which in rum may function as a kind of ?social support'. In the dyads, mainly one female kept contact to her bonding partner, i.e. she followed in most cases. Bonded females showed synchronous behaviours and their time-budgets were therefore very similar. The animals' activity depends on their age as well as on the keeping modus: Young animals were more active than the older animals, and activity in general was higher if the animals had the opportunity to graze or if they were fed several times during the day. Walker (1997) could also demonstrate that White rhinoceroses fed with gras are more active than when they were fed with hay. Feeding time increased during dispersed feeding, while time spent resting declined.
These results demonstrate that keeping conditions have an impact on the social behaviour of captive White rhinoceroses. The permanent presence of the male causes difficulties: Due to space-restrictions and the number of shadowed resting sites, feeding-sites, objects (such as tree-trunks, stones etc.) he is often forced to interfere with a female's individual distance. This interference causes aggression. Therefore, the keeping conditions should be improved with regard to the fact that both genders avoid each other, if the female is not (coming) into estrous.
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