Estimating abundance and population trends when detection is low and highly variable: A comparison of three methods for the Hermann's tortoise

摘要: Assessing population trends is a basic prerequisite to carrying out adequate conservation strategies. Selecting an appropriate method monitor animal populations can be challenging, particularly for low-detection species such as reptiles. This study compares 3 detection-corrected abundance methods (capture–recapture, distance sampling, and N-mixture) used assess size of the threatened Hermann's tortoise. We single dataset 432 adult tortoise observations collected at 118 sampling sites in Plaine des Maures, southeastern France. also 520 based on radiotelemetry data from 10 females estimate model availability (g0) needed sampling. evaluated bias N-mixture capture–recapture, by using simulations different values detection probabilities. Finally, we conducted power analysis ability detect changes abundances. The estimations obtained models were respectively 1.75 2.19 times less than those capture–recapture method. Our results indicated that g0 was influenced temperature variations differ same days. Simulations showed provide unstable with probabilities <0.5, whereas unbiased. Power none precise enough slow changes. recommend great care should taken when implementing monitoring designs large variation activity rates low Although are easy implement, would not them situations where probability very risk providing biased estimates. Among allowing estimation abundances, preferred trends. © 2013 Wildlife Society.