• complexity;
  • control;
  • environmental enrichment;
  • Old World primates;
  • ‘psychological space’;
  • substrate

Concern over the welfare of captive animals has resulted in the development of environmental enrichment procedures and studies into their effectiveness. Psychological and behavioural problems associated with captive primates, such as increased aggression and stereotypies, and physical problems, such as obesity and lack of muscle tone, need to be addressed if zoos are to maintain self-sustaining populations which exhibit the same behaviour patterns as those of wild conspecifics. Environmental enrichment should be a routine part of the daily husbandry schedules and all parameters which affect the primates should be enriched. Enclosure design, substrates and furnishings, social groupings, diet, novel objects, mixed-species exhibits and free-ranging areas are all discussed in this paper. Often, quick and easy forms of enrichment are the most effective, for example, filling a strong paper sack with straw and food treats can provide both a novel object and a food puzzle. Zoos should strive to carry out environmental enrichment, providing an interesting, stimulating and varying environment for their primates which. in turn. will enable zoos to fulfil their conservation, research, education and entertainment aims.