Flood Survival Strategies of Overwintering Snakes

Abstract

This thesis investigates snake flood survival during hibernation and how anthropogenic habitat alteration and climate variability may affect habitat quality and overwintering survival. Chapter one reviews the current understanding of ecophysiology of hibernation in snakes. In chapter two, I introduce a winter habitat model of a subterranean space that remains flood and frost-free, referred to as the “life zone,” where snakes survive winter. I analyzed 11- winters of hibernation habitat data and 18-yrs of population mark-recapture data to assess the effects of the first flood event on an endangered Massasauga population. Following the flood event, snake observations declined despite hundreds of hours of search-effort. At the population level this was evidence of poor winter survival and recruitment post flood. The direct cause of mortality was not determined but poor winter survival in areas with a depleted life zone was statistically supported. In the third chapter, I measured the metabolic rate (M ̇_(O_2 )) at 5°C for three snake species that inhabit my study area. I varied water level conditions and measured activity and dive behaviours continuously during experiments. I found differences between species in their resting metabolic rate, which I attributed to body size differences. I confirmed, cutaneous respiration occurs at a low rate and was significantly upregulated during a forced dive (flood event). Therefore, there is an intrinsic physiological response to a flood event in neonatal snakes. However, post-flood recovery indicated a greater oxygen demand after the short-forced dive. An oxygen debt was incurred during a short-forced dive under normoxic conditions. My conclusions are, 1) hibernation habitat (i.e., life zone) must include a non-freezing, non-flooding aerobic space throughout winter to maintain snake survival. 2) cutaneous respiration is a short-term flood survival strategy. I found no support for a complete aquatic hibernation strategy 3) the energy costs of a full-dive is additive to the recovery energetic costs of a flood event. A neonatal snake wintering energy budget is proposed, and winter mortality conservation issues are discussed in chapter 4.