Fourteen-Year Mark-Recapture Study on the Prairie Rattlesnake (Crotalus viridis viridis) in Northern Colorado
Mackessy, Stephen P.
School of Biological Sciences
University of Northern Colorado
Greeley, CO 80639 USA
Demographic information (e.g., population size, growth rate, sex ratio, reproduction and life span) provides critical pieces of information for the management and conservation of species. Mark-recapture studies are a useful tool for gathering this type of information for long-lived species. Despite the necessity of these studies, few long-term mark-recapture studies have been conducted on snakes. The Prairie Rattlesnake (Crotalus viridis viridis), an iconic species of the eastern plains of North America, is a long-lived and important component of the Colorado shortgrass-steppe ecosystem that hibernates in large numbers at stable refugia. For 14 years, two hibernacula in Weld County, Colorado have been part of a mark-recapture study of C. viridis. We analyzed demographic characteristics of this population, including hibernacula population size, sex ratios, body mass and size, tail length ratios, growth rates, size distribution, mass loss over hibernation, venom yield, capture rate, and den site fidelity. We explored the effects of temperature and precipitation on mass loss over hibernation. Overall, 1786 unique individuals have been captured, and 1003 have been captured more than once. The adult sex ratio (F:M) is 0.78:1; males are generally larger than females after their third year and produce more venom than females. Individual snout-vent lengths ranged from 155 to 1160 mm, and the longest inter-capture interval was 9 years. Neonates experience rapid initial growth during the first full season, which then slows as they age. This population exhibits high levels of den site fidelity, with snakes returning to the site of their original capture over 99% of the time. Demographic studies such as this can be invaluable for future animal conservation of snake species. Currently, these populations of C. v. viridis appear to be stable, but changes in land use, ownership, and or climate could adversely affect density and abundance, both locally and throughout its range.