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Social stress in captive slender lorises

Within family groups of lorises a rank order does not exist; under favourable conditions the animals coexist in a very peaceful manner, independantly minding their own business or joining for social activities. Food is shared and often taken away from each other without any problems. But if animals quarrel, the aggressive excitement of the superior animal may be enhanced to such a degree that it will chase the frightened opponent to complete exhaustion and even attack and bite a broom held between both. If the animals then are not separated in time, the weaker opponent may be killed, dying of stress and exhaustion or of the numerous small wounds caused by the adversary's teeth. The aggressor may be male or female; injuries are usually found in both opponents. Appeasing behaviours, turning away from the conspecific, feigning indifference and a monosyllabic hissing vocalization ("krik call"), most often used by males during estrous, apparently do not help if aggression exceeds a certain limit. But usually such extreme fights develop over the course of several days, thus allowing the keeper to interfere in time.

Behavioural signs of social stress

Some vocalisations, for instance sharp whistles or rhythmic chitter and cricket-like chirping and fast, jerky locomotion with rattling of twigs indicate an aggressive mood. Quarreling can be distinguished from playwrestling by loud vocalization and abrupt movements; sometimes the animals urinate or defecate with excitement. If animals, after usually sleeping huddled together during daytime, suddenly develop a tendency to sleep in separate places, this may indicate some social stress. Frequent or constant stay of an animal in the lower parts of the cage, without any obvious reason (as for instance looking for food on the ground) may be a sign of severe social stress, the weaker animal trying to avoid the aggressor who prefers the upper part of the cage. In this case, the animal often shows a typical posture (see figure), standing or sitting quietly, crouched with the head held low, the face turned upwards or quietly directed towards the aggressor with wide open eyes. If such a behaviour is observed, the animals should be separated at least for a limited time.
Pursuit of the female in the beginning of estrous is normal and can be recognized by frequent appeasing "krik" vocalization of the following male; some quarreling with agonistic vocalization in this period may be temporary and harmless. In case of doubt, random observation for signs of social stress or bite wounds, especially on hands and forearms, help to prevent severe injury.
At Ruhr-University there was no evidence of social stress caused merely by the frequency of interaction (crowding) as mentioned for Microcebus by Perret (1982); family groups up to eight animals showed friendly relations, frequent signs of wellbeing and regularly reproduced.

Possible causes of fighting

In our colony, unrelated adult lorises of the same sex were always unsociable. When animals are allowed to enter a new cage urine-marked by other lorises, aggressive behaviour against group members may result, especially in males smelling the urine of other males. (Some shy animals avoided empty cages recently urinemarked by strangers). If a male is sexually attracted by a female´s smell during estrous and excited, but the female rejects his approaches, quarreling may be the result. Some females defend their newborn babies against group members in the first few days after birth whereas others are rather tolerant; such postpartum aggression may lead to fierce quarreling, especially if a postpartum estrous occurs. When young males become mature, at the age of about 9 months, quarreling between father and son may occur (often, however, father-son-relation remained friendly until the youngster was taken out to avoid inbreeding). Environmental stress, hunger or vocalisation of fighting lorises in neighbouring cages may cause or enhance quarreling.

Measures to prevent problems caused by social stress

If animals quarrel, early feeding and availability of some food throughout the activity period is useful. Additional environmental stress which may aggravate aggressive excitement must be avided or at least minimized. Severe lesions and deaths are unlikely as long as the keeper separates the animals in time when signs of increasing aggressive excitement are noticed (fighting usually develops over a certain time, not suddenly). Separation before births as a precaution may be useful if the relations between the animals are not too good; in peaceful groups the presence of infants may cause very friendly social activities of all group members and separation is usually unnecessary. A well-furnished cage providing hideaways and possibilities to avoid each other is a good precondition for good social relations (see recomendations for cage construction and cage furnishing in the chapter about captive care).
 

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