Animals are frequently placed in zoos in unnatural habitats. Confined areas, little natural light, inadequate temperature control, improper diet and stress-inducing proximity of spectators, are some of the conditions experienced. Inadequate companionship of their kind and abuse by keepers are additional factors contributing to animal illness and mortality in zoological parks or research centres open to the public.
Of the tens of thousands of zoos worldwide, there are less than 50 with sufficient funds and expertise to provide adequate conditions for their animals. Large zoos are often willing to buy critically endangered species to enhance the prestige of their collection, even though they are aware that the species can only be obtained illegally. Private zoos have frequently been proved to be fronts for illegal animal-trafficking operations.
The life of most animals in captivity is an unusual one. Most animals are forced to make considerable adjustments to captive life. Furthermore, many of these creatures are captured as infants, which precludes satisfactory parental and hierarchical relationships during periods crucial for normal psychological development. This environmental upheaval is likely to have an important effect on behaviour, morbidity and mortality. For example, hypertension, gastric ulcers, eclampsia and remarkable cerebral arteriosclerosis are not unusual in captive primates.
Captive breeding programmes in zoos are often the only means whereby an endangered species can be saved, especially when their habitat is imminent danger of being destroyed.