Abstract
As Earth warms at an unprecedented rate, climatologists warn that droughts will become more frequent and more severe. Previous studies have shown that droughts have already produced profound detrimental effects on reproduction, foraging habits, diet, body condition, and mortality in a wide range of taxa. Yet identifying such effects is often difficult because we know so little about the ecology of so many species. Crotalus scutulatus, the Mohave Rattlesnake, is a medically important pit viper that is common in the deserts of the southwestern United States and northern México. Although it produces one of the most toxic venoms of any Nearctic snake and much has been published on its venom and bite, very little is known about its ecology. Pit vipers are underrepresented in the ecological literature, yet have been suggested as good model organisms for studies of the evolution of physiological processes and predator-prey relationships. Given its ecological niche as an ectothermic vertebrate predator in a near waterless environment, in addition to its notoriety as an understudied yet medically significant serpent, Crotalus scutulatus is an ideal subject for assessment of survival strategies during drought. Using radiotelemetry, I collected data during 2224 encounters with 68 male and non-reproductive female Crotalus scutulatus between 2002 and 2004 in southern California’s Mohave Desert. The area received only 21% of mean annual precipitation in 2002 but returned to 137% and 150% of mean in 2003 and 2004, respectively. The data were examined for behavioral differences between drought and non-drought periods in the context of recent and historical meteorological conditions, surface topography, floral associations, and sun position. The study animals relied on preformed body water in their prey as their primary water source. They were apparently obligate surface ambush hunters and remained on the surface to hunt, rather than retreating underground where rodent burrows offered lower thermal maxima and higher humidity that would have slowed evaporative water loss but where foraging success would have been reduced. Cutaneous evaporation represents ca. 75% of total evaporative water loss and is directly related to exposed surface area. The snakes reduced exposed skin by coiling and, when water stressed, by burying their coils in loose soil. They also sheltered behind the raised earthen mounds beneath creosote bushes (Larrea tridentata) and moved closer to these shrubs to escape wind and insolation, both of which increase cutaneous evaporation.