Nest predation is a major factor limiting breeding bird populations in primeval tree stands. Factors such as food limitation, availability of nesting sites or competition are not so important. Nest predation is usually more common along the edges of forests than in their interiors. The aim of this study was to determine how breeding losses in the secondary cavity-nester Collared Flycatcher Ficedula albicollis that bred in natural holes varied with distance from the forest edge in primeval stands of the Białowieża National Park (NE Poland). A comparison of the breeding losses along the edges and in the interiors revealed no statistical differences. The main nest predators were the forest species Apodemus flavicollis, Martes martes. and Dendrocopos major. It is better to keep forest tracts unfragmented, with a belt of bushes and thickets or woodland in an early successional stage along the edge. This would protect forest birds from predators living in open habitats.