Kernels Are Not Accurate Estimators of Home-range Size for Herpetofauna

Abstract

Kernel home-range estimators are becoming more widely used to determine the home-range size for herpetofauna, despite the problems associated with selecting the appropriate smoothing factor. We used simulations to demonstrate the inconsistency of kernel estimators at determining the home-range size of random distributions. Furthermore, we used the positions of ten adult male Lampropeltis triangulum radio-tracked over two full active seasons (2003 and 2004) to demonstrate that the size of the home range increases significantly with an increase in the smoothing factor. The degree of increase, however, was not consistent between individuals. In addition, using least-squares cross-validation to select the smoothing factor produced a wide range of values for different individuals. Because of these inconsistencies, we suggest using the minimum convex polygon (MCP) method to calculate home-range size in studies of herpetofauna. When studying habitat use, however, we suggest using the MCP as the area of the home range and adjusting the smoothing factor until the area of the 95% kernel equals the area of the MCP. This provides an objective method for selecting the smoothing factor.