Tiger Rattlesnake (Crotalus tigris) population demography based on 20 years of capture-recapture data


Goode, Matt

mgoode@arizona.edu


Pawlicki, Anthony

Wildlife Conservation and Management

School of Natural Resources and Environment

University of Arizona

Tucson, Arizona USA


Hanscom, Ryan

Department of Biology

San Diego State University

San Diego, California USA


Accurate estimation of demographic parameters is critical to our understanding of population dynamics, ecology, evolution of life history strategies, and effective conservation and management of wildlife populations. Reliable demographic parameter estimates rely on long-term monitoring data, typically consisting of marked individuals that are captured and recaptured over time. Although wildlife demography has focused primarily on game species, primarily to establish harvest limits, the need for robust monitoring and demographic analyses of non-game species has become increasingly common, especially for at-risk species. Among wildlife species, there remains an obvious lack of information regarding population demography of snakes. This lack of information is likely due to a combination of taxonomic chauvinism and the secretive nature of snakes, leading to low detection probabilities (i.e., low recapture rates) that produce parameter estimates with large error terms. Although considered rare, Tiger Rattlesnakes (Crotalus tigris) can be locally abundant, especially in rocky foothill environments in the Sonoran Desert. At our long-term study site near Tucson, where we have been studying the effects of urbanization on snakes and lizards since 2002, Tiger Rattlesnakes are the most common of 21 total snake species observed. From 2002-2021, we captured 877 Tiger Rattlesnakes, which we recaptured a total of 372 times (range 1-9). We produced annual estimates of population size/density, survival, and realized population growth using Program Mark and RMark. In addition, we examined the association of body size and growth with survival. We interpret results in the context of increasing urbanization and discuss insights into Tiger Rattlesnake ecology gleaned from demographic analyses.