To forage, mate or thermoregulate? Influence of food supplementation on behavior of the rattlesnake Sistrurus catenatus

Fitness is affected by resource needs driving behavior of cryptic ectotherms and requires trade-offs in activities such as foraging, locomotion and thermoregulation. However, the allocation of time and energy into such activities are often not well understood. Due to low energy demands and infrequent feeding, little is known about potential fitness trade-offs for temperate pitvipers which must balance remaining stationary to acquire and digest food while traversing large areas, particularly to procure mating opportunities. I radio-tracked 16 male Massasaugas (Sistrurus catenatus), an imperiled rattlesnake, from May to August 2014 in northern Michigan, half of which were fed a supplement diet of mice. I compared body condition as well as space and habitat use between the two treatments. Although open habitats were the highest in thermal quality, operative environmental temperatures that allowed Massasaugas to thermoregulate within their preferred range (30-33.6 °C) were uncommon overall in all habitats. Temperatures exceeding their challenging lower limit (19.9 °C), where they can still perform reasonably well, were much more typical. Relative to their availability across the study site, both fed and naturally foraging (control) snakes predominately used wetlands. Within the areas utilized by individual snakes, both groups used edges more than other habitats. Fed snakes were in better body condition than controls at the end of the study. Movement patterns and microhabitat selection of fed snakes did not differ from controls during the breeding season. Controls maintained higher diurnal body temperatures during the breeding season than fed snakes, but groups did not differ in their accuracy or effectiveness of thermoregulation during that time. Fed snakes did not increase body temperatures after feeding, perhaps because all of the snakes are already trying to maintain elevated temperatures in a thermally challenging environment. My results suggest movements associated with finding mates exert a significant pressure on male Massasaugas, causing them to forgo stationary digestion in exchange for increasing the prospect of reproducing. Given the infrequent reproductive rates of female Massasaugas in northern latitudes, intense mate searching by males may be a fixed behavior in these populations, regardless of food intake