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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.

Non-human primates occasionally exhibit behaviours thought to occur only in captivity that are considered abnormal. In particular, hair-plucking behaviour occurs across many species of mammals and birds. This study was the first to assess the phenomenology, demography and aetiology of this behaviour in captive gorillas across the Association of Zoos and Aquariums (AZA) population. A survey was sent to 52 AZA institutions housing western lowland gorillas. Hair-plucking behaviour occurred in 15% of the surveyed population with 62% of institutions housing a hair plucker. Individuals were most likely to self-pluck using their fingers. Individuals that were exposed as youngsters to a hair-plucking group member were significantly more likely to develop the behaviour themselves. There was also a trend toward solitary individuals being more likely to perform this behaviour. Future research needs include identifying hormonal correlates to this behaviour, understanding its relationship to acute or chronic stressors, and examining what causes this behaviour to fluctuate in frequency once it has developed.

One way to address the problem of small sample size in zoo research is to conduct a study involving multiple institutions. However, when conducting behavioral research, it can be difficult for one investigator to travel to each institution or for staff at individual institutions to find time to collect behavioral data. This study validates keeper assessments of western lowland gorilla ( Gorilla gorilla gorilla ) activity levels against behavioral data collected systematically in the zoo setting. Our purpose in validating a keeper rating of inactivity was to increase efficiency of behavioral data collection and maximize the amount of activity information for a larger study on gorilla health and behavior. A questionnaire was sent to 15 Association of Zoos and Aquariums (AZA) institutions housing 63 gorillas (37 male, 26 female) gorillas. Behavioral data for the project were collected by staff at each institution and/or by the principal invesitgator (PI) using group scan sampling. Every data collector was reliability tested by video until they gained >90% agreement with the PI. Mean percent of time spent in a behavior was calculated from the scan data. In this case, the focus was on the time spent immobile (i.e., stationary) and time spent idle (i.e., at rest, performing no otherwise defined active behaviors). We examined the correlation between the keepers' ratings and time spent immobile and idle as calculated from the behavioral data. Behavioral data on individuals that spent more time immobile were significantly correlated with an increasingly inactive ranking by staff ( P =0.003). Time spent idle was significantly correlated with time spent immobile ( P =0.001) and time spent idle was also significantly correlated with an increasingly inactive ranking by staff ( P

In both free-ranging and captive western lowland gorillas, a silverback provides protection and leadership, mediating conflict within a group. In the wild, when a dominant silverback dies the group will disperse or transfer to a solitary male, unless a subsequent male is present to inherit the group. In captivity, studies have focused on groups containing one male and therefore it is unclear how gorillas respond to the death or removal of a silverback in multi-male groups. This study examined the behavior of a bachelor group (Cleveland Metroparks Zoo) and a multi-male, mixed-sex group (Pittsburgh Zoo and PPG Aquarium) following the death of two older silverbacks in 2005. Both of the younger but dominant males maintained their same level of dominance after the death. We predicted that agonism would increase after the death as groups struggled for social stablility. We did observe an increase in both agonism and displacements among the bachelor group, but only observed an increase in displacements among the mixed-sex group. Although we predicted that there would be no change in solitary behavior, both groups decreased feeding and the mixed-sex group increased self-directed behavior post-death. In the bachelor group, self-directed behavior decreased and undesirable behavior increased. We also observed a difference in spatial distance after the death with members of the mixed-sex group becoming more dispersed and members of the bachelor group more converged. This study demonstrates that there is a period of transition for multi-male groups after the death or removal of the oldest silverback. Future research could integrate physiological measures with behavioral analyses before and after the death or removal of a prominent member of the group. Zoo Biol 29:16–29, 2010. © 2009 Wiley-Liss, Inc.