Effects of temperature and perch diameter on arboreal locomotion in the snake Elaphe guttata.

Arboreality is widespread in multiple lineages of snakes and these habitats are important for foraging, escaping predators, and thermoregulation for many species. However, very little is known about factors influencing the arboreal locomotor abilities of snakes. Arboreal performance was assessed in a semi-arboreal snake (Elaphe guttata) using an artificial perch apparatus. Locomotor velocity, body posture, and balance was measured during movement on three perch diameters (3, 6, 10-cm) at three temperatures (10, 20, 30 degrees C). Velocities attained by E. guttata on perches are much slower than those of terrestrial lateral undulation and swimming and somewhat slower than concertina velocities recorded in other species across the same experimental temperatures. At higher temperatures, faster speeds were associated with a more elongated posture. At lower temperatures, snakes displayed a more looped body posture, but still fell more often than at higher temperatures. Our results suggest that temperature has a large influence on both balance and movement by snakes on perches. Although there were no differences in velocities resulting from perch diameter, snakes fell more often from thicker perches. This differs from arboreal velocities attained by limbed vertebrates, which decrease with decreasing perch diameter, suggesting that snakes have a size-relative advantage over limbed animals, such as lizards, when traversing a network of narrow branches. Future studies investigating arboreal locomotion among snakes that vary both phylogenetically and morphologically are needed to assess the potential benefits of limblessness in complex, three-dimensional environments.