Variation in Defensive Behaviors of the Western Cottonmouth (Agkistrodon Piscivorus) as a Result of Temperature, Size, and Reproductive Condition

Date of Graduation

Fall 2007


Master of Science in Biology



Committee Chair

Brian Greene


Defensive responses during predatory encounters may vary according to the cost and benefits associated with different predatory contexts. In snakes, defensive behaviors may be influenced by temperature, sex, body size, and reproductive state. In response to human antagonists, the cottonmouth (Agkistrodon piscivorus) exhibits a flight response followed by a range of defensive displays which increase with the level of predatory threat. I utilized field and laboratory trials using a three-stage simulated predatory sequence where snakes were prodded, grasped, and finally, picked up to evaluate variation in the antipredator behavior of A. piscivorus as a function of temperature, body size, reproductive condition, and stimulus presentation sequence. Variation in antipredatory behavior was usually more apparent in active responses (bites and strikes) than passive displays, and was mainly explained by body size and body temperature. In laboratory-based repeated measures trials, snakes exhibited higher active defensive scores at 30°C than at 24°C. Paired comparisons of 20 adult females before and after parturition revealed a strong influence of reproductive condition with individuals exhibiting significantly greater active defensive responses when gravid. Randomization of the predatory sequence revealed that being prodded and grasped by the stimulus always elicited a stronger response by snakes than being picked up. However, snakes tested in the laboratory displayed much higher response scores upon initial approach than field-encountered snakes, suggesting that testing environment influenced snake behavior and that lab responses cannot be fully extrapolated to field situations.


cottonmouth, Agkistrodon piscivorus, defensive behavior, reproductive condition, temperature, predatory sequence

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© Diana E. Mullich