Operant Methodology Out Of The Lab and Applied To Enrichment With Captive Chimpanzees (Pan Troglodytes)

Abstract

A group of socially-housed chimpanzees, maintained in a zoo facility, were given the opportunity to access each of several purpose-designed and built enrichment items. Each item was made freely available in the chimpanzees' regular setting, with their normal activities available. The time members of the group spent engaging with each item gave an assessment of their relative preference for the items. The group were shown to have the greatest preference for a foraging enrichment item (Screwfeeder) and the least preference for an audiovisual enrichment item (TV/Video). Individual preferences for the items were evident. The chimpanzees were then taught to operate a weighted lever to get access to an item. Once all chimpanzees had operated the lever for access to the items, the number of lever operations required for access to each item was systematically doubled over a series of 3 hr sessions until the chimpanzees did not gain any access to that item for two consecutive sessions. One item was presented for two series of increases. The group response rates for an item increased with increased response requirement and then decreased with further increases, reflecting data from individuals in other research. The highest response requirement that maintained the group behaviour differed over the items. The number of times an item was accessed (consumption) was plotted against the response requirement (price) on logarithmic coordinates. Lines fitted to the data (demand functions) were shallowest for a foraging enrichment (Screwfeeder) and steepest for the audio enrichment (Musicbox). There were not enough data points to fit a function for the audiovisual enrichment. Differences in individual's demand within the group were evident. In general, the rank order of preference for the items and the rank order based on the parameters of the demand functions (slope or elasticity and initial intensity) was broadly the same. Three individual chimpanzees were exposed to two series of increasing response requirement for access to the Screwfeeder whilst housed alone, in one hour sessions. Response rates were again bitonic and the linear demand functions for these individuals were steeper (more elastic) than the functions fitted to data for group responding and differed idiosyncratically from the data for these individual when responding as part of the group. Thus the change of social setting had a different impact on the behaviour of each of the individuals. These results show that an animals‟ demand for a commodity is altered by the environment in which it is tested. ii Overall the research provides the first example of operant methodology in a zoo setting with a group of chimpanzees. It is also the first research to show differential responding for access to different enrichment items by a group and how this relates to their preference (based on time allocation) for those items.