REPRODUCTION AND FOOD OF THE BUZZARD BUTEO-BUTEO IN RELATION TO THE ABUNDANCE OF RODENTS AND BIRDS IN BIALOWIEZA-NATIONAL-PARK, POLAND

A population of migratory Buzzards Buteo buteo breeding in the pristine deciduous forests of the Bialowieza National Park (eastern Poland) was studied in 1986-1989. Breeding densities were 4.5-5.2 pairs/10 km2. Mean clutch size was 2.4 eggs (n = 22), from which 1.9 young hatched, and 1.3 juveniles fledged per breeding pair. Breeding performance of pairs with territories located near the forest edge was positively correlated with the cyclic abundance of Microtus spp. in the open river valley and meadows. During the breeding season Buzzards fed primarily on birds (42-75% of prey biomass), rodents (10-26%), and moles (7-23%). Variation in the proportion of rodents in the diet during May-July was not related to the changes in either Microtus or Clethrionomys and Apodemus numbers. From the bird community living in the Bialowieza National Park, Buzzards selectively preyed on medium-sized birds, particularly Turdus philomelos and woodpeckers, and neglected very numerous small passerines. At least 40% of the birds taken by Buzzards were juveniles or fledglings.