Rain-harvesting by the Southwestern Speckled Rattlesnake (crotalus Mitchellii Pyrrhus)

Acquiring water is a challenge for desert animals, and organisms inhabiting arid regions have evolved morphological, physiological, and behavioral traits to maintain an appropriate water balance. On four occasions, I observed rain-harvesting or observed behaviors suggestive of rain harvesting in a population of speckled rattlesnakes (Crotalus mitchellii) in the Mojave Desert of southwestern North America. Snakes collected rainwater on the surface of their bodies and subsequently drank it. Speckled rattlesnakes also drank rainwater that accumulated in structural features of their habitat (e.g., surface of rocks). My observations suggest that C. mitchellii may engage in rain-harvesting when thermal conditions are not optimal (i.e., during cold temperatures). For instance, rattlesnakes presumably emerge from hibernation to take advantage of rainwater. RESUMEN—Adquirir agua es una demanda importante para animales del desierto, y los organismos de zonas áridas han evolucionado caracterı́sticas morfológicas, fisiológicas y de comportamiento para mantener un balance de agua apropiado. En cuatro ocasiones observé la conducta de recolección de agua de lluvia, o conducta que sugiere la recolección de agua de lluvia, en una población de vı́bora de cascabel (Crotalus mitchellii) del desierto de Mojave, en el suroeste de Norteamérica. Las serpientes colectaron el agua de lluvia en la superficie de sus cuerpos y luego se la tomaron. Las vı́boras de cascabel también tomaron agua de lluvia que se acumulaba en estructuras de su hábitat (por ejemplo, en la superficie de las rocas). Mis observaciones sugieren que C. mitchellii quizás colecta agua de lluvia cuando las condiciones termales no son óptimas (es decir, cuando las temperaturas son bajas). Por ejemplo, las vı́boras de cascabel presumiblemente interrumpen su invernación para tomar agua de lluvia. Acquiring (or conserving) water is a challenge for desert animals. Consequently, organisms inhabiting arid regions have evolved a variety of physiological, morphological, and behavioral traits to maintain an appropriate water balance (Costa, 1995; Bradshaw, 1997). Rain-harvesting is a mechanism by which animals first collect water on the surface of their bodies during rainfall, and subsequently drink it (Sherbrooke, 1990). This water-collecting technique has been reported in several species of reptiles, including lizards (Bentley and Blumer, 1962; Schwenk and Greene, 1987; Sherbrooke, 1990, 1993, 2004; Peterson, 1998; Veselý and Modrý, 2002), turtles (Auffenberg, 1963), and snakes (Louw, 1972; Robinson and Hugues, 1978; Miller, 1985; Greene, 1997). Recently, this behavior was first described in free-ranging populations of three species of rattlesnakes, the midget-faded rattlesnake (Crotalus oreganus concolor; Ashton and Johnson, 1998), the Mojave rattlesnake (Crotalus scutulatus; Cardwell, 2006), and the western THE SOUTHWESTERN NATURALIST 54(4):518–521 518 The Southwestern Naturalist vol. 54, no. 4