Survival of Timber Rattlesnakes (Crotalus horridus): Investigating Individual, Environmental, and Ecological Effects

A major effort in species conservation is the construction of life-history models to better predict, identify, and respond to population changes. Yet demographic studies linking individual, environmental, and ecological factors to survival are rare. We used radio telemetry to monitor 47 adult Timber Rattlesnakes (Crotalus horridus) during five active seasons and four overwinter periods from April 2007– November 2011 in south-central Indiana, USA. The study period serendipitously encompassed an oak (Quercus spp.) mast failure and subsequent 50% decline in prey abundance, allowing us to test hypotheses about ecological effects on survival. We detected 10 mortalities. The causes of mortality during active seasons included predation (n 5 5), human persecution (n 5 2), and vehicle strike (n 5 1). Variation in active season survival was explained best by the interaction of sex and prey availability along with an effect of marking cohort. Seasonal survival estimates ranged from 0.720–0.983 with female survival decreasing by at least 15% the year after prey availability declined. Overwinter survival was high in general (n 5 2 mortalities), with estimates weakly affected by sex (male 5 0.966; female 5 0.990) and decreasing slightly with colder monthly temperatures. Although ecological effects were most powerful in our study, 30% of mortalities were associated with human activities. Focused education and outreach efforts may be useful for improving survival of Timber Rattlesnakes.