A Radio-Tracking Study of the Ranging Behaviour and Dispersion of European Sparrowhawks Accipiter nisus

Abstract

SUMMARY (1) The ranging behaviour of sparrowhawks was studied by radio-tracking in two areas 12 km apart, one rich in prey and the other poor. (2) In both areas, ranges of adults centred around nesting areas (and in winter around nearby roosts) in woodland. (3) Range size was smallest when hawks were attending the nest, from pre-lay through to incubation/brooding, and largest outside the breeding season; it was most variable at seasons when range size was rapidly changing, in early spring and (for hens) in the late nestling and post-fledging periods. The ranges of cocks were on average smaller than those of hens, and for the same sex and season, ranges were greater in the area with low prey density than in the area with high prey density. (4) In their first winter, both cocks and hens were less faithful to any particular roost than were adults; they had more roost sites and used the main site less often. There was a suggestion that adults used their main roost less often when their ranges were large. (5) When hunting, sparrowhawks used woodland more than expected from its proportion in their ranges, particularly broadleaved woodland, and hens used open country (especially farmland) more than cocks. Adults mostly roosted in thick conifer woodland near nesting areas, and returned repeatedly to the same sites, whereas first-year birds in winter roosted in a variety of small woods in open country, both during the day and overnight. (6) At some stages of breeding, range parameters could be related to breeding performance. In the pre-lay period, cocks which had small ranges and spent much time near the nesting area became successfully mated, whereas cocks which had large ranges and spent little time near the nesting area remained unmated. In the late nestling period, the range size of hens was negatively correlated with the growth of their young. Provision by us of supplementary food in both periods resulted in hens becoming more sedentary at the nest.