The neck flattening defensive behaviour in snakes: First record of hooding in the South American colubrid genus Philodryas

Abstract

Animal species have evolved a remarkable diversity of defensive phenotypic strategies aimed to deceive predators and other forms of danger. By relying on deception, these adaptations increase the chances of avoiding physical contact that may otherwise have very high fitness costs. One such deceptive behaviour is the popularly-known neck flattening, or “hooding”, observed in some snakes. Hooding consists in the lateral expansion and dorso-ventral flattening of the neck, which creates the impression of a bigger opponent during confrontations. This trait is highly characteristic of cobras (Elapidae family). However, neck flattening is not exclusive to elapids, and has in fact been observed in a few other snake lineages, including some species of the families Lamprophiidae and Colubridae. Here, we present the first report of hooding behaviour in the South American colubrid genus Philodryas, based on field observations conducted on the Chilean species P. chamissonis (the long-tailed snake). Our report adds to the few cases in which this deceptive behaviour has been observed in snakes outside the cobra family.