Mortality patterns and the cost of reproduction in a northern population of Ratsnakes, Elaphe obsoleta

A recent study of Ratsnakes (Elaphe obsoleta) in Texas found that adult mortality was higher for females than males, consistent with the cost of reproduction in snakes being higher for females. To determine whether the same pattern prevailed in a northern population of Ratsnakes, we used data collected using radio-telemetry to test several predictions of the cost-of-reproduction hypothesis. Contrary to there being a cost to reproduction, mortality rates did not differ between juvenile and adult snakes and, contrary to females having a higher cost of reproduction, mortality rates among adults did not differ between males and females. The only evidence consistent with reproduction increasing mortality risk was higher winter mortality for females in poor condition following egg laying. Mortality did not vary with activity but increased with time spent basking, although group differences in basking were not sufficient to produce differences in mortality. High risk of winter mortality in this population may require all Ratsnakes to behave in ways that mask mortality costs associated with reproduction. To determine whether our results for Ratsnakes in Ontario are anomalous or reflect something more substantial about the cost of reproduction in snakes, details of mortality patterns from more species, ideally with diverse ecologies, are needed.