Nash, R., Johnston, H., Robbins, A. et al. 2021. The effect of enrichment filling and engagement time on regurgitation and reingestion behaviour in three zoo-housed orangutans. Journal of Zoological and Botanical Gardens 2(1), 10–20.

Regurgitation and reingestion (R/R) is a prevalent, abnormal behaviour observed in captive great apes. R/R may be related to animal welfare and while less R/R appears to occur when apes are provided with browse and continuous foraging opportunities, the aetiology of the behaviour (e.g., foraging time or taste characteristics such as sweetness) is not well understood. This study aimed to determine how environmental enrichment may affect R/R in three zoo-housed, adult orangutans. Over eight weeks, nine fillable enrichment items were provided twice to each orangutan–once with a sweet filling and once with a savoury filling. Enrichment engagement time and R/R behaviour were monitored for 1-h after the item was provided. Individual differences were found in R/R occurrence. One individual was more likely to perform R/R when given enrichment with a sweet filling (p < 0.05), and a second was more likely to R/R with savoury filled enrichment (p < 0.05). R/R behaviour from the third orangutan was unaffected by enrichment filling (p > 0.05), however he engaged longer with savoury filled enrichment, compared to sweet (p < 0.05). No relationship was found between engagement time and amount of R/R behaviour, for any of the orangutans (p > 0.05). While these results should not be generalized without a larger study, they do suggest that diet and enrichment qualities may play a role in the performance of R/R, and individual variation should not be overlooked when considering causation.