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Apparent Rain Harvesting by a Colorado Desert Sidewinder (Crotalus cerastes laterorepens)


Jim Rorabaugh
U.S. Fish and Wildlife Service
Tucson, Arizona

The Yuma Desert is the hottest and driest portion on the Sonoran Desert in Arizona. Mean annual precipation is about 2.8 in. at Yuma and a scant 2.2 in. at the San Luis Rio Colorado in the very northwestern corner of Sonora, Mexico.

Temperatures frequently exceed 109°F on summer days. These conditions are harsh for reptiles, but the situation is exacerbated by the fine silica sand substrates that characterize the area. These fine sands quickly absorb any precipitation. As a result, there is no pooling water, no arroyos that collect surface flows, and no zero-riparian corridors. Instead, there are just miles and miles of sandy flats and occcasional dunes vegetated primarily by sparse associations of creosote, white bursage, and galleta grass. These conditions make it very challenging for reptiles or other animals to obtain free water for drinking.

During mid-April of 2007, I participated in Transect work in the Yuma Desert to quantify levels and types of human distrubance. In the early morning, as I was walking as I was walking a section located just north of the international boundary and about 12.7 miles northeast of the Colorado River at San Luis, Az., I encountered a Colorado Desert Sidewinder in a loose coil that was markedly flattened out against the sand. The air and surface temperatures were 59°F and a light rain was falling. No annual plants were present, indicating that the winter of 2006-2007 had been relatively dry. I was surprised to see a snake in the cool, wet weather, and its flattened posture was curious as well. Although individuals can sometimes be found cratered in the sand on cool days, suitable surface temperatures for sidewinder activity are typically 68°F. I stopped to take out my camera and document this behavior, but the snake quickly disappeared into a nearby burrow before I could take a picture. About 10 minutes later, I encountered a second sidewinder. This individual was smaller, but was also in a loose coil and flattened against the sand. I was able to take several pictures of this specimen. Although I did not see this snake actually drinking (moving its jaws), I believe it was likely drinking water from its skin. Its snout was directed into the inside of a coil of its body that would be an efficient place to collect rainwater accumulating and running off its skin. The flattening of its body, clearly visable to me, would also facilitate water collection.

Drinking of water in this way has not previously been documented in Crotalus cerastes, however, it is not unprecedented for snakes or reptiles in general. On page 32 of Harry Greene's "Snakes, the Evolution of Mystery in Nature" a Horned Adder (Bitus caudalis). an evolutionary equivalent to the sidewinder from Southern Africa, is pictured drinking water from its skin in a pose very similar to the sidewinder I observed. Peringuey's Adder (Bitus peringueyz), another African sidewinder equivalent, flattens its neck to condense coastal desert fog for drinking. Drinking from skin has also been documented in the Great Basin Rattlesnake and Lasiewski and Bartholomew suggested Desert Night Lizards and Western Banded Geckos may do the same. The Texas Horned lizard has been observed to arch its back during storms to allow rainwater to flow towards its mouth; Johnson and Spicer reported the same behavior in a captive Flat-tailed Horned Lizard that was misted with water. In the Yuma Desert where free water is in scarce supply, sidewinders likely obtain much of their water metabolically from the foods they eat; however, rain harvesting during infrequent precipitation events may be important for maintenance of homeostasis in the very arid enviroment that is their home.

This paper was originally published in Sonoran Herpetologist, the Journal of the Tucson Herpetological Society on 20 Dec 2007.

Date submitted 01 Apr 2008

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