In arboreal habitats gaps between branches and branch structure profoundly affect the ability of animals to move; hence, an ability to perceive such attributes could facilitate choosing routes that enhance the speed and ease of locomotion. Although many snakes are arboreal, no previous study has determined whether they can perceive structural variation of branches that is mechanically relevant to their locomotion. We tested whether the gap distance, location, and attributes of two destination perches on the far side of a crossable gap affected the route travelled by North American rat snakes (Pantherophis), which are proficient climbers. Snakes usually chose routes with shorter gaps. Within a horizontal plane, the snakes usually went straight rather than crossing an equal distance gap with a 90° turn, which was consistent with our finding that crossing a straight gap was easier. However, decreasing the distance of the gap with a 90° turn eliminated the preference for going straight. Additional factors, such as the width of the landing surface and the complexity of branching of the destination perches, resulted in non-random route choice. Thus, many of the observed biases in route choice suggested abilities to perceive structural variation and select routes that are mechanically beneficial.
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E. Buschbeck, J. Layne, M. Riley and G. Byrnes provided helpful comments, suggestions, and direction. B. Murphy, Z. Jones, M. Herrmann, J. Olberding and A. Sturbaum provided assistance with experiments. This work was funded by a grant from the Wiemen-Wendell-Benedict Fund of the University of Cincinnati, Department of Biological Sciences to RHM and by National Science Foundation grant IOS 0843197 to BCJ. Care and treatment of the snakes were approved by the Institutional Animal Care Use Committee (protocol number 07-01-08-01) of the University of Cincinnati, and the principles of laboratory animal care (NIH publication No. 85-23, revised 1985) were followed.
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