The Collared Flycatcher Ficedula albicollis population nesting in natural cavities in the Białowieża National Park was studied during 1988-1994. In none of the 534 cases, when a Collared Flycatcher was seen entering a natural cavity, was it killed. Additionally, in less than 2% (10/534) of observations did the male enter cavities owned by a different bird species. We suggest that competition for nest boxes should be interpreted very carefully because in parts of Europe where the experiments were carried out, many environmental characteristics have been profoundly altered by man.