Three-dimensional locations of destinations have species-dependent effects on the choice of paths and the gap-bridging performance of arboreal snakes.

Challenges for moving in arboreal environments include sizable gaps and variable three-dimensional locations between the discrete destinations created by branches. Different three-dimensional orientations of the body change the mechanical demands of crossing gaps, especially for elongate animals, but these effects on both the maximal gap distance crossed (Gapmax ) and the choice of destinations are poorly understood despite many animals frequently encountering these circumstances. We tested and compared the effects of three-dimensional gap location on the bridging ability of three species of snakes with similar length but moderately stout (Boa constrictor), intermediate (Pantherophis guttatus) or slender (Boiga irregularis) shapes, and we tested for bias in choice of destinations for the latter two species. The effects of both gap location and species on Gapmax were highly significant, and the rank order of species from greatest to least Gapmax was often from the most slender to the stoutest species. Although the effects of yaw (horizontal) angles were statistically significant, they were small compared to those of pitch (vertical) angles, which created nearly twofold variation in the values of Gapmax within each species. The greatest values of Gapmax occurred when snakes went straight down. Within a horizontal plane, P. guttatus and B. irregularis had similar preferences for choosing gaps with smaller yaw angles. However, when pitch angle was varied, P. guttatus preferred lower destinations, whereas B. irregularis preferred higher destinations. Thus, despite quite uniform effects of gap location on bridging abilities and torques acting on the animals, some preferences for locations were species specific. J. Exp. Zool. 319A:124-137, 2013. © 2012 Wiley Periodicals, Inc.