Detecting Long-Term Population Trends for an Elusive Reptile Species

Many reptile species are in decline and turtles are especially susceptible. In Massachusetts, eastern box turtle (Terrapene carolina carolina) population densities are critically low, and they are listed as a Species of Special Concern. To aid in the conservation of this species, we developed a statewide population monitoring program to track large-scale population trends. We used GENPRES3 to identify the most efficient sampling design a priori. Using this design, we performed visual surveys in 2010-2012 and used site occupancy models to evaluate baseline occupancy and abundance data. We surveyed 62 4-ha monitoring plots within early successional and forest edge habitat where box turtles congregate in the spring for foraging, mating, nesting, and thermoregulation. We also used radio-telemetry at 2 survey sites to evaluate assumptions and further assess occupancy rates, detection estimates, and population size. The best fit Royle-Nichols model predicted a probability of box turtle occupancy of 0.81 +/- 0.10 (mean +/- SE) and a mean probability of detection of 0.29 +/- 0.18. Roads and vegetation density were important covariates affecting the probability of occurrence. Survey start time, humidity, and surveyor were important covariates affecting detection probability. A power analysis indicated that we could detect a 10% decline in occupancy between 5-year sampling rounds within 15 years. The proportion of radio-tagged turtles inside the survey plots during surveys was relatively constant at each site (0.44-0.63 and 0.36-0.43), mean detection rate was 0.35 +/- 0.10, and the total estimated population size of the 2 survey plots (8 ha total) was 13.31 +/- 1.53. Our results can be used to track the status of this rare species as well as guide conservation actions and evaluate the effectiveness of site-specific and statewide management plans. Our approach and design can serve as a model for other states developing monitoring programs for the eastern box turtle and other similar, rare and difficult to detect species. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.