Meeting Abstract
In arboreal habitats, diverse animals encounter discrete choices between branches with variable structure that has predictable consequences for the ease and speed of movement. Many species of snakes are arboreal, and previous studies found that some species use visual cues to choose between alternative destinations when bridging gaps. For example, brown tree snakes prefer destinations that are wider, closer, and along a straighter trajectory, all of which are biomechanically advantageous. Whether attributes of destinations that are unrelated to mechanical demands affect perch preference remains poorly understood. Hence, we manipulated perch color, background color, perch structure, and perch location to test their effects on perch choice of brown tree snakes bridging gaps. For destinations with identical perch structure, gap distance and trajectories (yaw angle = 45 deg), the snakes preferred black perches rather than white perches when the background was white, but the snakes unexpectedly continued to prefer black rather than white perches when the background was black. The following two cases illustrate how a bias for black perches superseded a bias for a mechanically beneficial perch. First, with a white background and identical trajectories, the snakes preferred a black perch with a 47 cm gap rather than a white perch with a 37 cm gap. Second, a wider white perch was not preferred to a narrower black perch. However, a preference for a straighter trajectory persisted even when the destination with 0 deg yaw was white and the black perch required a 90 deg turn. Our results emphasize that visual cues unrelated to the physical structure of surfaces can bias choice and in some cases supersede a preference for mechanically beneficial surfaces. However, such attributes of locomotor surfaces have largely been ignored.
