The Effect of Reproductive Condition on the Thermal and Spatial Ecology of the Female Cottonmouth (Agkistrodon Piscivorus) in Southwest Missouri

Females of many temperate snake species are known to exhibit thermophilic behavior during gestation, resulting in differential habitat use of gravid and non-gravid individuals. I investigated the influence of thermoregulation on spatial patterns and habitat use of 16 female cottonmouths (Agkistrodon piscivorus) near the northwestern limit of the species’ range in southwest Missouri during late summer. All snaked exhibited similar body temperature profiles characterized by a warming period in the late morning to a plateau maintained through mid-day, followed by a gradual decline from late afternoon into the evening. Preferred body temperatures measured in a laboratory thermal gradient were higher for gravid than non-gravid snakes. Physical models demonstrated that preferred temperatures were available to snakes in all habitat types but that habitat thermal quality differed as a function of variance in operative temperatures within habitat types. Gravid females were extremely sedentary and restricted all activity to patchy rocky outcroppings. These areas had the highest thermal quality of all available habitats, providing a thermal gradient that allowed snakes to maintain preferred body temperatures. As a result, gravid females maintained higher field body temperatures than non-gravid females which resided in forest habitats with lower and more variable environmental temperatures. My data on narrow prefers for thermally favorable habitats, combined with female-biased melanism in northern populations, suggest that exploitation of thermoregulatory opportunities is important to gravid A. piscivorus at the northern periphery of its range