Kuhar, C. W., Smith, K., Soltis, J. 2008. The visitor effect on apes: real or imaginary? Enriching or stressful? American Journal of Primatology 70(S1), 23 (31st Meeting of the American Society of Primatologists Scientific Program, Abstract #8).

The “visitor effect” problem, whether zoo visitors are stressful or enriching to zoo animals, is made difficult to analyze by numerous methodological challenges. The extremes in visitor attendance patterns during the holiday season at Disney’s Animal Kingdom® have provided a unique “natural” experiment where animals can experience large and small crowds over a short period, thereby controlling for other confounds, such as season or day of the week. We have examined the impact of visitors on gorilla (Gorilla g. gorilla, n=10), siamang (Hylobates syndactylus, n=3), and white-cheeked gibbon (Hylobates leucogenys, n=4) behavior using group scans and all-occurrence scoring of social behaviors. Through a series of studies we have shown that solitary behavior patterns do not differ by crowd size, although there is a great deal of individual variation. Some age-sex classes, i.e. young adult males, appear to be more influenced by visitor numbers and respond to these with increased aggression. However, increased aggression is not a consistent finding across any of these species. Interestingly, animals tended to occupy areas further removed from but did not completely move out of sight of zoo visitors. This implies that zoo animals may find these visitors enriching, particularly if they are able to control the number and context of the observations or interactions. This suggests that zoo exhibits should be built to provide animals opportunities for choice of locations and the opportunity to control stimulus inputs.