2.2 Estimation of home range, cumulative distance travelled and site fidelity
We estimated annual and monthly home-ranges using the 95% kernel density estimator contours (KDE) and the cumulative distance travelled for each tagged individual using the “amt” package (Signer et al., 2019). Cumulative distance travelled per month were measured as the total length of each track (in km) (Edelhoff et al., 2016). Individuals with less than ten fixes per day were discarded (n=4 cases).
We measured the individual home-range fidelity by calculating the percentage of overlap between consecutive monthly home-range (Fieberg & Kochanny, 2005). We selected the 95% KDE as an estimator of home-range to evaluate differences in foraging areas. The percentage of overlap was quantified using the Bhattacharyya coefficient, which ranges between 0 (complete segregation) and 1 (perfect overlapping; Fieberg & Kochanny, 2005; Winner et al., 2018).