Throughout history not only domestic animals as pets and livestock were kept in captivity and under human care, but also wild animals. Some were failed domestication attempts. Also, in past times, primarily the wealthy, aristocrats and kings collected wild animals for various reasons. Contrary to domestication, the ferociousness and natural behaviour of the wild animals were preserved and exhibited. Today's zoos claim other reasons for keeping animals under human care: conservation, education and science.
Captive animals, especially those not domesticated, sometimes develop abnormal behaviours.
One type of abnormal behaviour is stereotypical behaviors, i.e. repetitive and apparently purposeless motor behaviors. Examples of stereotypical behaviours include pacing, self-injury, route tracing and excessive self-grooming. These behaviors are associated with stress and lack of stimulation. Many who keep animals in captivity attempt to prevent or decrease stereotypical behavior by introducing stimuli, a process known as environmental enrichment.
A type of abnormal behavior shown in captive animals is self-injurious behavior (SIB). Self-injurious behavior indicates any activity that involves biting, scratching, hitting, hair plucking, or eye poke that may result in injuring oneself. Although its reported incidence is low, self-injurious behavior is observed across a range of primate species, especially when they experience social isolation in infancy. Self-bite involves biting one’s own body—typically the arms, legs, shoulders, or genitals. Threat bite involves biting one’s own body—typically the hand, wrist, or forearm—while staring at the observer, conspecific, or mirror in a threatening manner. Self-hit involves striking oneself on any part of the body. Eye poking is a behavior (widely observed in primates) that presses the knuckle or finger into the orbital space above the eye socket. Hair plucking is a jerking motion applied to one’s own hair with hands or teeth, resulting in its excessive removal.
The proximal causes of self-injurious behavior have been widely studied in captive primates; either social or nonsocial factors can trigger this type of behavior. Social factors include changes in group composition, stress, separation from the group, approaches by or aggression from members of other groups, conspecific male individuals nearby, separation from females, and removal from the group. Social isolation, particularly disruptions of early mother-rearing experiences, is an important risk factor. Studies have suggested that, although mother-reared rhesus macaques still exhibit some self-injurious behaviors, nursery-reared rhesus macaques are much more likely to self-abuse than mother-reared ones. Nonsocial factors include the presence of a small cut, a wound or irritant, cold weather, human contact, and frequent zoo visitors. For example, a study has shown that zoo visitor density positively correlates with the number of gorillas banging on the barrier, and that low zoo visitor density caused gorillas to behave in a more relaxed way. Captive animals often cannot escape the attention and disruption caused by the general public, and the stress resulting from this lack of environmental control may lead to an increased rate of self-injurious behaviors.