Comparison of two sampling protocols and four home-range estimators using radio-tracking data from urban badgers
Radio-telemetry is often the method of choice for studies of species whose behaviour is difficult to observe directly. However, considerable debate has ensued about the best way of deriving home-range estimates. In recent years, kernel estimators have become the most widely used method, together with the oldest and simplest method, the minimum convex polygon. More recently, it has been suggested that the local convex hull might be more appropriate than kernel methods in cases where an animal's home range includes a priori inaccessible areas. Yet another method, the Brownian bridge, explicitly uses autocorrelated data to determine movement paths and, ultimately, home-ranges or migration routes of animals. Whereas several studies have used simulation techniques to compare these different methods, few have used data from real animals. We used radio-telemetric data from urban badgers Meles meles to compare two sampling protocols (10-min versus at least 30-min inter-fix intervals) and four home-ranges estimators (minimum convex polygons, kernels, convex hulls, and Brownian bridges). We used a multi-response permutation procedure and randomisation tests to compare overall patterns of fixes and degree of overlap of home-ranges estimated using data from different sampling protocols, and a general linear model to compare the influence of sampling protocols and home-range estimator on the size of habitat patches. The shape of the estimated home ranges was influenced by sampling protocol in some cases. By contrast, the sizes and proportions of different habitats within home ranges were influenced by estimator type but not by sampling protocol. Convex hulls performed consistently better than kernels, and are especially appropriate for patchy study areas containing frequent no-go zones. However, we recommend using convex hulls in combination with other methods to estimate total range size, since convex hulls tended to produce smaller estimates than any other method. Results relating to Brownian bridges are preliminary but suggest that this method is unsuitable for species in which range size is small compared to average travel speed.
Key words: Brownian bridge, local convex hull, Eurasian badger, fixed kernel, MCP, Meles meles, radio-telemetry