Development of demographic models to analyze populations with multi-year data—Using Agassiz’s Desert Tortoise (Gopherus agassizii) as a case study

First posted August 27, 2021 For additional information, contact: Director,Western Ecological Research CenterU.S. Geological Survey3020 State University Drive EastSacramento, California 95819 We developed a model for analyzing multi-year demographic data long-lived animals and used from population of Agassiz’s desert tortoise (Gopherus agassizii) at the Desert Tortoise Natural Area in western Mojave as case study. The study area was 7.77 square kilometers included two locations: inside outside fenced boundary. wildlife-permeable, protective fence designed to prevent entry vehicle users sheep grazing. collected mark-recapture 1,123 tortoises during seven annual surveys consisting censuses each over 34-year period. Additional were when marked recovered dead removed between survey years. Bayesian modeling framework develop multistate Jolly-Seber because its ability handle unobserved (latent) states modified this incorporate non-survey Three size-age (juvenile, immature, adult), sex (female, male), location (inside boundary), three survival (not-yet-entered, entered/alive, dead/removed) incorporated into model. calculated densities estimated probabilities growth one state larger state, after 1 year 5 years, detection. Our results show declining with low estimates probability move boundary greater than outside. detecting differed by lowest smallest highest adult tortoises. can be analyze other animal populations where vital rates are expected vary depending on multiple individual states.