A population of migratory BuzzardsButeo buteobreeding in the pristine deciduous forests ol the Białowieża National Park (eastern Poland) was studied in 1986–1989. Bleeding 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 ofMicrotusspp. 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 lo the changes in eitherMicrotusorClethrionomysandApodemusnumbers. From the bird community living in the Białowieża National Park, Buzzards selectively preyed on medium-sized birds, particularlyTurdus philomelosand woodpeckers, and neglected very numerous small passerines. At least 40% of the birds taken by Buzzards were juveniles or fledglings.