You "R/R" What You Eat: Effects of High-Fiber, Low-Starch Diet Change on Regurgitation and Reingestion and Coprophagy in Zoo-Housed Gorillas

Regurgitation and reingestion (R/R) and coprophagy are common behaviors exhibited by primates living in human care. To reduce this undesirable behavior in two troops of western lowland gorillas (Gorilla gorilla gorilla), the diet was modified by increasing fiber (by increasing browse) and decreasing starch (by reducing but not eliminating biscuits). We monitored behavior before, 3 weeks after, and 1 year after the diet change. One year after the diet change, the family group's diet was modified by adding more fruit to facilitate training. We documented significantly increased feeding activity for both troops, with time spent feeding doubling for one troop. Some individuals initially increased R/R or coprophagy behaviors but these increases were not significant, and 1 year after the diet change R/R was significantly reduced in the silverback male who had been known to exhibit R/R up to multiple times per day. In the family troop, coprophagy later decreased when animals were reunited and spent more time outdoors (for reasons unrelated to the diet change study), but this was not significant. This is the first published study to assess the behavioral effects of a high-fiber, low-starch diet on gorillas one full year after the diet change was made, and we demonstrated that the diet continued to positively impact some individuals' behavior. We discuss implications of our findings and suggest future directions for institutions that seek to reduce these behaviors in primates without necessarily completely eliminating biscuits from their diets.