Implementing a low‐starch biscuit‐free diet in zoo gorillas: The impact on behavior

Abstract

In the wild, western lowland gorillas travel long distances while foraging and consume a diet high in fiber and low in caloric density. In contrast, gorillas in zoos typically consume a diet that is low in fiber and calorically dense. Some items commonly used in captive gorilla diets contain high levels of starch and sugars, which are present at low levels in the natural diet of gorillas. Diet items high in simple carbohydrates are associated with obesity and heart disease in humans. Typical captive gorilla diets may also encourage undesirable behaviors. In response to these issues, we tested the behavioral impact of a diet that was biscuit-free, had low caloric density, and which was higher in volume at five institutions. We hypothesized that this diet change would reduce abnormal behaviors such as regurgitation and reingestion (R/R), decrease time spent inactive, and increase time spent feeding. The biscuit-free diet significantly reduced (and in the case of one zoo eliminated) R/R and may have reduced hair-plucking behavior. However, an increase in coprophagy was observed in many individuals following the diet change. The experimental diet caused a general increase in time the gorillas spent feeding, but this increase did not occur across all institutions and varied by individual. Interestingly, the overall time gorillas spent inactive actually increased with this diet change. Future research will examine these behavioral changes in a greater number of individuals to determine if the results remain consistent with these preliminary findings. Additionally, future research will examine the physiological impact of this diet change.

Behavioral and hormonal responses to the availability of forage material in Western lowland gorillas (Gorilla gorilla gorilla)

“…The amount of time the gorillas performed feeding‐related behaviors (ingesting, food processing, or foraging) was significantly increased by both mulberry and alfalfa. Alfalfa more than doubled the amount of time spent feeding compared to no forage material, reaching estimates close to those for wild Western lowland gorillas (Magliocca & Gautier‐Hion, ; Remis, ) and on the high end of ranges reported for zoo‐housed gorillas on a biscuit‐free diet (Less, Bergl, et al, ). Alfalfa increased feeding bout durations the most, while mulberry elicited the most food processing behavior.…”

“…Social and undesirable behaviors were recorded on scans to create a complete activity budget but were not statistically analyzed here. The ethogram (Table ) was adapted from Stoinski, Kuhar, Lukas, and Maple, () and Less, Bergl, et al (). All‐occurrence behaviors were scored in bouts, wherein 5 s had to elapse between successive presentations of the same behavior to qualify as a new bout (Stoinski et al, ).…”

“…In recent years, practices for feeding captive wildlife have shifted beyond nutritionally standardizing diets to naturalizing their composition and presentation as well (e.g., Less, Bergl, et al, ; Ruskell, Meiers, Jenkins, & Santymire, ; Williams, Cabana, & Nekaris, ). There is greater recognition that nutritional and behavioral impacts of feeding regimens may not always align.…”

“…Differences in activity budgets between captive and wild gorillas can also be traced to feeding behaviors. Gorillas in zoos spend, on average, 9–36% of their time feeding and foraging and, in turn, spend a greater percentage of time inactive than wild gorillas (Less, Bergl, et al, ). Estimates for the amount of time spent feeding and foraging for wild Western lowland gorillas range from 54% of the time (Remis, ) to 72% at forest clearings containing mineral‐rich plants (Magliocca & Gautier‐Hion, ).…”

“…Adding more woody browse and reducing quantities of fruit in the diet reduces R&R (Lukas, ), as does feeding high‐fiber biscuits (Remis & Dierenfeld, ). Less, Bergl, et al () experimentally transitioned gorillas in five zoos to a diet free of biscuits with reduced fruit and increased amounts of leafy greens and alfalfa hay. Although the biscuit‐free diet did not impact activity levels, it had positive effects on rates of R&R and hair‐plucking (Less, Bergl, et al, ).…”