Should I Stay or Should I Go? Spatial Ecology of Western Chicken Turtles (Deirochelys reticularia miaria)

Authors: Brandon C. Bowers, Danielle K. Walkup, Toby J. Hibbitts, Paul S. Crump, Wade A. Ryberg, A. Michelle Lawing, Roel R. Lopez

Though its distribution within Texas is widespread, the spatial resource requirements of the Western Chicken Turtle (Deirochelys reticularia miaria) are poorly understood. Formal protection is lacking for the subspecies and its habitat, and past research suggests that its remaining habitat in Texas is under threat from increasing urbanization. For these reasons, the U.S. Fish and Wildlife Service issued a 90-day finding that states listing the subspecies as Threatened or Endangered may be warranted. Here, we present analyses of telemetry data using a variety of methods to understand annual home range, core activity area, and movements. We evaluate the applicability of Minimum Convex Polygons, Kernel Density Estimators, and Autocorrelated Kernel
Density Estimators to a species that migrates between isolated wetlands, spending most of the year aestivating underground. To improve model fit, we applied each method to datasets with all positions included, repeated consecutive coordinates excluded, and with only aquatic positions included. The 95% Kernel Density Estimators provided the most consistent estimates of annual home range. Traditional 50% core activity area estimators had questionable utility, and we observed better geographic fit for core activity areas in 95% Kernel Density Estimates using the least-squares cross validation on the aquatic dataset. When making habitat conservation decisions, managers should consider how extensive periods at rest affects home range estimates, how periods of drought affect movement, and how the longevity of the species, the potential to make long migrations over land, and the landscape characteristics of the site could affect spatial resource requirements.

Suggested Citation