The Christmas Island blue-tailed skink (Cryptoblepharus egeriae): a survey protocol and an assessment of factors that relate to occupancy and detection

WA Museum Records and Supplements | Updated 8 years ago

ABSTRACT – The endemic Christmas Island blue-tailed skink (Cryptoblepharus egeriae) is in serious decline and only one known population remains on Christmas Island, despite it being widespread and common up until the 1990s. Here, we examine the relationship between occupancy, detectability, and several key environmental predictors and describe a passive observation survey protocol for the species that incorporates detection probabilities. By incorporating several covariates on detection and occupancy that we, a priori, considered to be important, we found C. egeriae was more likely to be found in habitat with an intermediate canopy cover. Detection probability using our survey protocol (0.28 with 95% CI: 0.17 to 0.43) was weakly but positively related to survey hour (10:00 to 14:00 local time), indicating afternoons were a better time to survey. Based upon a value of 0.28, we predict that four to five survey visits over a reasonably short period of time (≈ one month) will suffi ciently minimise the likelihood of recording a false absence for the species.