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 pristin e deciduous forests of the Bialowieza National Park (eastern Poland) w as 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 cor related with the cyclic abundance of Microtus spp. in the open river v alley and meadows. During the breeding season Buzzards fed primarily o n 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 wa s not related to the changes in either Microtus or Clethrionomys and A podemus numbers. From the bird community living in the Bialowieza Nati onal Park, Buzzards selectively preyed on medium-sized birds, particul arly Turdus philomelos and woodpeckers, and neglected very numerous sm all passerines. At least 40% of the birds taken by Buzzards were juven iles or fledglings.