Opdam P. (1975) Inter- and intraspecific differentation with respect to feeding ecology in two sympatric species of the genus Accipiter. ARDEA 63 (1-2): 30-54

Two sympatric, closely related hawk species, Accipiter nisus (Sparrowhawk) and Accipiter gentilis (Goshawk), have similar hunting techniques and habitat choice, but species as well as sexes differ considerably in size (Table 1). The question is raised whether each Accipiter size-group selects a characteristic range of prey-size. Samples have been obtained from the diet of both hawks by collecting feathers and hair that remained from their prey. The habit +of the Sparrowhawks to visit particular plucking sites in winter permitted separation of the samples according to sex by direct observations. Moreover, when compared with each other the samples from periods of hunting and non-hunting activity of the females revealed data on the food of the sexes separately in the reproductive period. Body-weight of the prey appeared to be related to predator-size (Tables 3 and 6, Figs. 1 and 3). In winter the diets of the Accipiter groups were distinctly separated (Fig. 2), but during the reproductive season this differentiation diminished considerably (Fig. 5). In winter the sexes of the Sparrowhawk showed a somewhat different habitat choice, which was closely linked up with the habitat preference of their main prey species. It is concluded that each Accipiter group occupies a somewhat different niche, intraspecific overlap being more extended than interspecific overlap. Niche-breadth decreased under poor food conditions (in winter).