Reaching new heights: the effect of an environmentally enhanced outdoor enclosure on gibbons in a zoo setting.

Gibbons have adapted to live in the canopy layer of the rainforest. Gibbons in the wild predominantly spend their time high in the trees resting, traveling, and foraging for food. Comparatively, gibbons in the zoo often rest and search for their food terrestrially. The purpose of this study was to provide these arboreal smaller apes with more opportunities to utilize more vertical space. Six gibbons (4 Nomascus leucogenys and 2 Symphalangus syndactylus) were observed in 2 phases of an observational study. The 1st phase measured space utilization and behaviors of the zoo-housed gibbons in their original outdoor enclosures using instantaneous sampling. The 2nd phase measured the same space usage and behaviors after several modifications were made to the environmental structures in the same outdoor enclosures. A 2-way mixed-model analysis of variance tested the height utilization of the 6 gibbons. The gibbons chose to spend significantly more time outside and at higher heights when the new structures were added. This study shows that given the opportunity, gibbons will exhibit more species-appropriate behaviors.