Article Review: Prey Choice in Crotalus horridus

            A study published in the Journal of Herpetology last year investigated the relationship between ambush behavior and prey frequencies in Crotalus horridus.  Some prey species targeted by rattlesnakes are arboreal, while some use fallen logs to move across the forest floor, and the snakes presumably use different hunting strategies to target them.  The results suggest that timber rattlesnakes alter their hunting strategies in order to capture specific prey.

            Rattlesnakes are known to use several ambush postures when hunting.  For this study, the authors defined three categories: log-oriented, when the snake was coiled and facing a fallen log or branch; non-log-oriented, when the snake was coiled but not facing any structure; and vertical-tree, when the snake was coiled at the base of a tree and facing upward.  Snakes were tagged with radio transmitters and located periodically to record their hunting behavior.  The researchers also collected fecal samples to determine which species the snakes were eating and used average weights of the species to estimate the snakes’ biomass intake.  Small mammal surveys of the area were done using drift fences and baited traps.

Vertical-tree orientation was the most common ambush posture, and gray squirrels made up the largest percentage of the diet.  Because this posture is only beneficial for catching arboreal animals and not ground-dwelling mammals such as mice, the authors conclude that the snakes are exhibiting prey choice and targeting larger mammals.  This indicates that rattlesnakes do not passively sit in frequented areas and strike at any prey that passes, but instead select ambush locations based on which prey would be most beneficial to them.  However, the researchers base this conclusion partly on the fact that they did not catch any squirrels in their mammal survey, so squirrels must be less common than mice and shrews in the ecosystem.  I found myself questioning the effectiveness of their traps.  The authors also suggest that prey choice may be related to body size, but since their snakes all relatively similar in size, another study would be required to confirm the relationship.  Future studies could also compare northern populations with southern populations, since southern snakes tend to be larger.  If prey choice is related to local habitat makeup as well as a snake’s morphology, comparing populations with reference to habitat type (forest vs. grasses) and prey composition could be especially enlightening.

Reference:

S. M. Goetz, C. E. Petersen, R.K. Rose, J. D. Kleopfer, & A. H. Savitzky. Diet and Foraging Behaviors of Timber Rattlesnakes, Crotalus horridus, in Eastern Virginia. Journal of Herpetology 50: 520-526. https://doi.org/10.1670/15-086.