Where are my dragons? Replicating refugia to enhance the detection probability of an endangered cryptic reptile

Abstract

Rare and cryptic species require effective monitoring methods in order to track populations over time. Monitoring surveys utilizing artificial refugia are an increasingly applied tool for detecting herpetofauna; yet for many species, limited information is available on the factors that influence optimal detectability. Most monitoring programs utilize only one type of artificial refuge. This approach has limitations as it may overlook the dynamic habitat needs of some species, with different refugia required under different conditions. Here we investigate whether using two different types of artificial refugia could maximize overall detection of the endangered Monaro grassland earless dragon Tympanocryptis osbornei by providing refugia that match habitat use. Tympanocryptis osbornei is a grassland specialist endemic to the Monaro Plains of southern NSW which occurs within a fragmented and altered agricultural landscape. Artificial refuge habitat in the form of customized replica ‘spider’ tubes and concrete roof tiles were utilized to infer the highest detection probability when compared to traditional rock rolling techniques. We found tubes to be more successful than tiles (mean: 0.021, 0.010–0.037 95% Bayesian credible interval (BCI) vs mean: 0.0096, 0.0045–0.018 95% BCI). However, this was dependent on air temperature, as tiles became more effective between 25 and 30 °C when dragons were more likely to be using surface shelters. Artificial refugia on a transect level (12 tubes and 12 tiles) had the greatest detection probability (mean: 0.11, 0.04–0.23 95% BCI) compared to individually checked objects. Our results identify the best current methods and conditions to detect T. osbornei and provide insights into additional considerations for optimizing survey efforts, timing, and detectability for other small reptiles in temperate climates. We recommend a combination of artificial refugia be considered in future surveys for cryptic reptiles.