Twig mimics

Natural History, Dec, 2001 by Kirsten L. Weir

TWIG MIMICS Reptiles have evolved an assortment of strategies for discouraging, avoiding, or escaping from predators. Certain snakes have bright colors that warn of venom; others feign death when threatened. Many lizards have sharp spines, and some attempt to frighten predators with sounds. Still others opt to run away and hide.

Andreas Schmitz and Mark Auliya, from the Zoologisches Forschungsinstitut und Museum Alexander Koenig in Bonn, Germany, recently described the unusual escape tactics of the shy diurnal skink Sphenomorphus sabanus. Auliya observed this behavior in a swampy forest in West Kalimantan, Indonesia, while he was studying another reptile species. One night he happened to see, by the glow of a flashlight, an S. sabanus scampering along the branch of a tree, attempting to flee. Then it stopped suddenly and hung upside down; clinging to the branch with its hind claws, the lizard resembled a small, dry twig. After a few moments, it stopped doing its twig impression and darted away. The finding was hardly a surprise to local villagers--they confirmed that these slinks use imitation to avoid detection.

Even though a few species of geckos also mimic twigs or leaves to avoid predators, the strategy is quite rare. Most lizards that reside in trees drop to the ground when threatened. The researchers suggest that the advantage of S. sabanus's escape route may be its novelty. If predatory birds expect their prey to fall to the ground, Schmitz and Auliya's argument runs, they would be unlikely to notice a lizard still hanging from a branch. The cryptic posture might make these skinks invisible to tree-dwelling predators as well. ("An Unusual Escape Reaction Observed in Sphenomorphus sabanus [Reptilia: Scincidae] in Indonesia, With Taxonomic Comments," Herpetological Bulletin 76, 2001)