Volume 6 (2010) Pages T1-T9
We developed methods to estimate the home ranges and important foraging areas of Northern Goshawks Accipiter gentilis, based on nest distributions, vegetation, and land-use patterns. We assessed the reliability of the estimation method by using radio-telemetry data on movements and locations of 19 pairs of Goshawks.
The assessment shows that the home ranges can be determined by Voronoi Partitioning based on the nest distributions. The important foraging areas were determined by the following steps. We first divided a goshawk home range map, including vegetation types and land-use, into a grid of 250 m x 250 m cells, and calculated the area of open habitat within 150 m of a woodland edge in each grid cell. The cells were then designated with a value weighted by the distance from a goshawk nest using seven weighting categories. We hypothesized that areas surrounded by grid cells within the upper 25 % of the resulting value ranges were important foraging areas (see Fig 4).
The estimated home ranges included 86.7% of perching locations on average, as determined by radio-telemetry location data. The important foraging areas that resulted from the estimation included 92.1% of 50% Kernel home range as determined through radio-telemetry. It is therefore reasonable to assume that the method based on an evaluation of nest distribution, vegetation and land-use does provide a reliable estimation of the home range and important foraging area for Northern Goshawk.