This study is based on an analysis of nest-histories of 652 Collared Flycatcher nests found in natural tree cavities in the Białowieża National Park in 1988–1999. The secondary-cavity-nester Collared Flycatcher constitutes migratory single-brooded population breeding in high density in the primeval oak-lime-hornbeam (Querco/TillioCarpinetum) stands. Nest predation was the main reason of the breeding losses (240 nests) accounting for 91% (82%–100%) of them. Local production of fledglings was affected by nest predation caused by rodents, mustelids and Great Spotted Woodpecker. In this study a link between forest rodent cycles and the Collared Flycatcher fluctuations in number was documented. Number of produced fledglings depended on both, positively the number of the Collared Flycatcher breeding pairs in year N and negatively on the Yellow-necked Mouse density in year N. Rate of nest destruction is related to the density of the Yellow-necked Mouse recorded in BNP, while independent on the Collared Flycatcher density (nest predation limiting but not regulating). The predation pressure in some years keeps the Collared Flycatcher density at a level well below that of the potential the habitat resources (nest-sites, food). Local breeding density was shaped by fledglings productivity (breeding success) of the previous year. Earlier hypotheses concerning the Collared Flycatcher and other birds population limitation were also discussed.