An analysis of regurgitation and reingestion in captive chimpanzees

The abnormal behavioral. pattern of regurgitation and reingestion (R/R) is poorly understood in chimpanzees (Pan troglodytes). This study assesses R/R in 13 indoor-housed chimpanzees living in pairs and trios. Focal animal sampling data were used to calculate scores for R/R, two other classes of abnormal behavior (abnormal behaviors with oral components and those without oral components), and affiliative social behavior. R/R was observed in 85% of study subjects, an elevated proportion in comparison to a previously published survey of captive chimpanzee populations. Contexts and temporal patterns of R/R suggest that detection of this behavior may in many cases require observations outside of daily management routines. Social disturbances did not elicit this behavior. Statistical tests showed no relationship between individual differences in R/R rates and rates of other abnormal behavior classes, time engaged in affiliative behaviors, number of cagemates or housing history; nor were sex differences detected. Meal composition was not found to effect the time devoted to R/R. Statistical tests did show a strong positive relationship between rates of R/R and elapsed time since feeding. These results suggest that increasing meal frequency or providing consistently available edible material may prove more broadly effective than altering meal composition. Temporal distributions of R/R differed from those of abnormal behaviors, suggesting that factors such as boredom, hunger or other sources of stress may differentially affect the expression of various classes of abnormal behavior.