Rain harvesting behavior in free-ranging Prairie Rattlesnakes (Crotalus viridis)
Department of Biology
Carlisle, Pennsylvania USA
Organisms inhabiting xeric environments face many challenges to obtain dietary water. Numerous species have evolved unique adaptations to collect, harvest, and condense water from infrequent and unpredictable rainfall. Several snake species have been documented collecting and drinking precipitation from their skin, referred to as rain harvesting behavior. In some areas of their range, Prairie Rattlesnakes (Crotalus viridis) inhabit environments with soil that has poor water retention properties, and therefore may have evolved and adapted to obtain dietary water through harvesting rain. We designed an experiment to elicit and observe rain harvesting behavior (RHB) in Prairie rattlesnakes in their natural environments. Using a hand-held pump sprayer, we sprayed snakes with short bursts of water to simulate rainfall and recorded their behavior using a Canon EOS 80D Digital SLR camera with a 28-300 mm zoom lens. In a two week period between 25 May and 5 June 2021, we obtained 72 videos of 94 snakes (70 free-ranging snakes). Using these videos, we described rain harvesting behavior using a six-phase illustrated ethogram. Various postures and movements (e.g. tongue flicking rates, head angles, drinking surfaces, body positions, etc.) were quantified using Tracker, ImageJ, and R. Our results show that Prairie Rattlesnakes harvest rain from themselves, neighboring snakes, and non-snake surfaces. Snakes coiled in concentric, overlapping coils and dorsoventrally flattened (despite uneven substrates) when drinking from themselves. Prairie Rattlesnakes exhibited various head angles dependent on drinking surface, presumably to maximize water intake. Snakes were also noted to drink with their heads elevated and no labial contact to a specific surface; suggestive of drinking water run-off from the head. This observation supports previous descriptions of interscalar channels exhibiting capillary action directing water more efficiently to the mouth in Phrynosoma cornutum and Moloch horridus. This research serves as a baseline for further understanding rain harvesting in desert-inhabiting species. Furthermore, we introduce several hypotheses to explain dorsoventral flattening variation, drinking from non-snake surfaces, drinking with the head elevated and no labial contact to a surface, and drinking from neighboring snakes.