Estimates of Survival Probability from Two Populations of Giant Gartersnakes in California’s Great Central Valley

Abstract

The loss and modification of freshwater ecosystems has led to high rates of imperilment for freshwater species. The Giant Gartersnake (Thamnophis gigas) is among the species that have suffered declines in abundance and spatial distribution and is currently listed as a threatened species by the U.S. government and the State of California. Conservation and management of populations of T. gigas are hampered by a lack of information on its demography. Without estimates of demographic parameters, the status of the population is difficult to characterize, and identifying the parameters to target in management planning is problematic. We used capture–recapture data from two populations in the Great Central Valley of California to estimate annual survival probability. We also evaluated hypothesized causes of variation in survival probability among individuals and among years. Model-selection results for the population in the American Basin indicated that females have a higher survival probability than males and t...