Description:
Methods of censusing breeding raptors are reviewed and discussed on the basis of field experience gained mainly in Uusimaa, southern Finland, during the last ten years. The four commonest diurnal raptors of the region, the Honey Buzzard Pernis apivorus, the Goshawk Accipiter gentilis, the Sparrowhawk A. nisus and the Common Buzzard Buteo buteo were included in the study. No single general census method is equally applicable to them all. Specialized habitat requirements of the Accipiter species, and clearly discernible courtship flight of the buzzards as well as other observations (moulted feathers, remnants of prey and faeces) are useful keys for the location of occupied territories. The breeding part of the population can be censused reliably only on the basis of occupied nests and fledged broods still fed by their parents. The densities of the species were estimated as follows: the Honey Buzzard 9—11 pairs/100 km2, the Goshawk 5—8 pairs/100 km2, the Sparrowhawk about 9 pairs/100 km2 and the Common Buzzard 7—22 pairs/100 km2. The local variation in raptor densities may be pronounced even in relatively small areas, probably largely due to differences in the combination of habitats available. Annual fluctuations in numbers and in the proportion of non-breeders may also be considerable.