Do thermal cues influence the defensive strike of cottonmouths (Agkistrodon piscivorus)?

Abstract

Crotaline snakes (family Viperidae, subfamily Crotalinae) are unique among snakes in the possession of facial pits situated on each side of the head between the nostril and the eye (Klauber, 1972). These organs are depressions with highly innervated membranes at their bases that have a heat-sensing function and that transmit information to the part of the brain that receives visual data (Desmoulins, 1824; Bullock and Diecke, 1956; Barrett, 1970; Hartline et al., 1978). Thus, pitvipers can detect temperatures through the radiant heat energy emitted by objects and/or organisms relative to the background temperature. This thermoreceptive sense is not specific to crotalines: some booids also have the capacity to detect temperature variation but the thermal receptors are situated on the labial scales, and hence are called labial pits. The significance of this thermoreceptive organ on the predatory strike of booid and viperid snakes has been established (De Cock Buning, 1983; Kardong and Mackessy, 1991; Shine and Sun, 2003). However, no evidence has been provided on alternative functional roles played by thermal pits (Greene, 1992), specifically on defense. It has been suggested that thermal pits might help snakes in detecting predators (De Cock Buning, 1983), in finding optimal basking sites for thermoregulation (Goris and Nomoto, 1967; Herbert and Hayes, 1992), and in locating winter dens (Sexton et al., 1992). Because we lack empirical studies on the role of these pits in a non-predatory context, this study provides further understanding on