The Role of Temperature in Habitat Selection by Eastern Massasauga Rattlesnakes (Sistrurus Catenatus Catenatus) Near Their Northern Range Limit

163 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Temperature should be one of the most important factors influencing habitat selection in terrestrial ectotherms, because physiological processes depend on body temperature and body temperatures depend primarily on the habitats they occupy. The importance of temperature in habitat selection should be amplified in cool climates and for ambush predators, who must select habitat warm enough to detect and strike prey quickly. Using 4 years of telemetry data from 34 individuals, I investigated the role of temperature in habitat selection by eastern massasauga rattlesnakes (Sistrurus c. catenatus ) on the Bruce Peninsula, Ontario, near their northern range limit. Snakes were selective at the microhabitat scale, preferentially using locations with closer retreat sites and shrubs than random. Gravid females were most selective, using sites with more rock cover and less canopy closure than sites used by males and nongravid females. Landscape-scale habitat preferences were proportional to the availability of suitable microhabitat. The overwinter mortality rate (23% over 3 years) was among the highest reported for north-temperature vipers. Lethally low temperatures were a lesser concern for snakes during the active season than temperatures routinely too low for basic functions like prey capture and reproduction. Consistent with theory, snakes thermoregulated less accurately (i.e., body temperatures were further from preferred levels) when environmental temperatures were low, but thermoregulatory effort (i.e., how close body temperatures were to preferred levels, relative to environmental temperatures) varied with environmental temperature in different ways for different snakes. Gravid females maintained body temperatures suitable for embryogenesis by using sites with little forest cover and basking more when environmental temperatures were very low. Males and nongravid females did not make similar adjustments, and in fact used more ground cover (hindering thermoregulation) when environmental temperatures were very low. Gravid females may be required to bear the costs of a high thermoregulatory effort (e.g., reduced foraging success, increased predation risk) to successfully reproduce in an environment with a short and cool active season. Cold incubation conditions, a short time window between parturition and hibernation, and cold overwintering conditions likely result in high rates of neonate mortality, possibly limiting the northern distribution of massasauga rattlesnakes.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD