Demography of a Small and Isolated Population of Eastern Massasauga Rattlesnakes (Sistrurus catenatus) Threatened by Vegetative Succession

Reforestation of early successional vegetation types has been implicated in the decline and extirpation of snake species dependent on exposed basking sites. Consequently, basking-site improvement measures (e.g., brush clearing) are frequently proposed to conserve threatened and endangered snake populations; however, demographic response of snakes to vegetation manipulation is largely unknown. This study measured changes in reproductive fitness, survival, and abundance of females in an isolated population of endangered Eastern Massasauga Rattlesnakes (Sistrurus catenatus) in years before and after cutting of woody vegetation to create basking opportunities. We marked a total of 181 snakes from 2006 to 2014, over which time substantial vegetation was cleared in key gestation areas to increase availability of basking sites for gravid females. Reproductive cycles of females in this population appeared to be primarily biennial, with parturition dates strongly influenced by maximum daily summer temperatures. Estimated annual survival (s = 0.78, 95% confidence interval: 0.67-0.86) and number of gravid females (range = 9-46 individuals) showed no temporal trend, nor did body condition (mass relative to length) of gravid females. Our results imply that if a demographic response to basking-site manipulations occurs in Eastern Massasauga Rattlesnakes, it will significantly lag management intervention.