Abnormal behaviour in captive lorises and pottos

Natural behaviour is regarded as adaptive in the evolutionary sense (advantageous for the individual´s fitness) in a natural environment. Under captive conditions, "unnatural" behaviours may occur which are not observed in the wild but are advantageous and therefore regarded as normal in the captive environment. Behaviour may be regarded as "abnormal" if it is not part of the normal behaviour and no function, goal or benefit for the acting individual can be recognized, if the behaviour is disadvantageous or injurious for the animal or if elements of normal behaviour are performed in an inappropriate manner (inappropriate with regard to context, sequencing, frequency or duration) ⁵⁵. Erwin and Deni (1979) give a review of behavioural disturbance occurring in primates ⁵⁶.

Trollope (1977) ⁵³ saw no abnormal behaviour in 20 Lemuridae and 10 Lorisidae observed. In Loris tardigradus, evident stereotyped movements are rare. Two of about 70 observed animals, both very active males, repeatedly showed stereotyped locomotor patterns in certain places in their cages which looked like somersaulting ¹⁵. Both were housed in large, well-furnished cages which is in accordance with findings of Trollope (1977) ⁵³ that abnormal behaviour in primates was highly correlated with social conditions, but not with cage furniture. More frequent and less conspicuous behavioural disturbances in Loris are excessive food consumption with subsequent adiposity (observed in some very active and curious animals) and passiveness (usually in females), which may also lead to adiposity. Most probably boredom and inadequate social conditions were the causes. Overgrooming leading to some damage of the fur (see fig. 4 a) occurred in four cases. From Otolemur crassicaudatus, overgrooming and subsequent formation of gastric trichobezoars or even self-mutilation (gnawing of the own extremities) were reported, possibly due to boredom or stress in relatively small cages ¹⁰; self-mutilation is not known from Loris. Chewing of non-edible parts of the cage furniture such as artificial plants occurs in some cages, possibly a sign of playful mind or boredom. Hyperaggressivity has occurred in young loris males; it was apparently caused by excitement when unexperienced animals were introduced to a mate. In two cases, after treatment with tranquilizer the formerly hyperaggressive animals showed a normal social and sexual behaviour in the same situation, in one case tranquilizer had no positive effect; this animal was kept solitary for some time and later, without further social experience, showed a normal appeasing and mating behaviour towards females. Hyperaggressivity in such cases might possibly be matter of age (tendency to find and conquer an own territory after leaving the mother?).

According to Mitchell (1970) ⁵⁴, it may be important to distinguish between transient effects dependant on processes in the environment and long-lasting behavioural deficiencies, based on permanent anomalies within the animal itself. In the slender lorises of Ruhr-University, all observed behavioural abnormalities were transient and vanished after some social or environmental changes or behavioural enrichment.