Using 3D Photogrammetry to Quantify Usable Space in Zoo-Housed Primate Habitats

Studies of zoo animal space use typically use ground-level measurements as a proxy for "usable space," but this method ignores above ground areas that are behaviorally relevant to arboreal species. Previous work has proposed different methods to calculate usable above ground space, but each has presented different limitations, ranging from the estimation of areas of dense complexity to the significant manual effort needed to physically measure spaces. To address these limitations, we tested a new, 3D photogrammetry-based method ("3DP method") for calculating usable space in the habitats of two zoo-housed primate species (crowned lemur [Eulemur coronatus], and Bornean orangutan [Pongo pygmaeus]). 3D photogrammetry generates a 3D point cloud and subsequent mesh, using physically captured images, with geometric, measurable properties. Our method was compared to a previously published method, based in SketchUp, ("MSU method") for both quantification of usable space (surface area, volume) and efficiency of model generation (active and passive work required). The 3DP method generated similar results for both usable surface area and volume for the crowned lemur habitat, while requiring 82% less active work from the user. Furthermore, the 3DP method was able to calculate usable space in a habitat (Bornean orangutan) that was 13,274% larger than the crowned lemur habitat, and substantially larger than any habitat where the MSU method has been applied in published work. Overall, the 3DP method decreased the ratio of active to passive work required for calculating usable space in zoo habitats with complex vertical space, and is flexible enough to be applied to habitats of varying sizes.