How Color Affects Choice of Branches by Snakes

Abstract

By Trey Saunders, Biology of Animals

Advisor: Bruce Jayne

Presentation ID: AM_ATRIUM23

Abstract: Many animals live and move in trees, including many species of snakes, all of which have elongate bodies that are well suited for reaching across the gaps between branches. Previous studies have found that brown tree snakes use visual cues to select between two alternative branches when they cross gaps, and they prefer wider branches or darker branches when the alternative is mechanically equivalent. To test the generality of using such visual cues to choose between two alternative branches while crossing gaps, we studied boa constrictors, which are phylogenetically distant compared to brown tree snakes. Similar to previous findings, when both destination branches had the same color, boa constrictors preferred destinations that were wider or easier to reach as a result of being either closer or along a straighter trajectory. In addition to preferring the destinations that conveyed biomechanical advantages, the boa constrictors also preferred darker rather than lighter surfaces when the two alternative destinations were mechanically equivalent. The bias for a darker surface was so strong that in some cases it eliminated the preference for choosing a lighter, identically shaped destination that was closer than the darker alternative. Similarly, the preference for a darker surface overrode the preference for choosing a destination that was wider or along a straight trajectory (rather than requiring a 90-degree turn). This study nicely illustrates how a sensory bias that is independent of the mechanical attributes of a surface can profoundly affect where animals choose to go.