Gilloux, I., Gurnell, J., Shepherdson, D. 1992. An enrichment device for great apes. Animal Welfare 1(4), 279-289.

The influence of an environmental enrichment feeding device (puzzle feeder), on activity and behaviour patterns of captive orang-utans, gorillas and chimpanzees was studied at London Zoo. General activity levels and behaviours directed towards the feeder increased for all species when the feeder was filled with food. Chimpanzees used the feeder significantly more (18% of observation periods) than either gorillas (10%) or orang-utans (9.4%).There was considerable individual variation of puzzle use by individuals within each group and time of day also affected use. In some instances abnormal behaviours were reduced. These results are discussed in relation to the management of captive great apes and it is suggested that the use of puzzle feeders can improve the welfare of these animals.