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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.
Three species of cavity nesters potentially competitive with the Starling — the Great Spotted Woodpecker Dendrocopos major, Middle Spotted Woodpecker D. medius and Nuthatch Sitta europaea were studied in the years 1997-1999. The number of suitable nest sites for Starlings and competitive pressure were manipulated by increasing or decreasing the availability of nest boxes. Increased nest-site competition did not lead to significant changes in number among the studied species. The Starling was found to take over up to 25% of holes chosen by Nuthatches for breeding. Increased availability of nest sites did not protect Nuthatches from cavity losses, but reduced their frequency. Only 20% of Nuthatch pairs that lost their holes renested successfully in the same breeding season. No impact of Starlings on breeding woodpeckers was noted.
We studied the fluctuation in 1975-1997 numbers of two species: the Pied Flycatcher Ficedula hypoleuca and the Collared Flycatcher F. albicollis breeding in natural cavities in the primeval deciduous stands of the Białowieża National Park (NE Poland). Both studied birds are commonly regarded as competitors if sympatric. Densities of two flycatchers are positively correlated within 7 plots (pooled data) investigated by a territory mapping method over 22 years (r = 0.71, p < 0.05) and 36 ha plot studied very intensively through 9 years (r = 0.35, p < 0.05). We found no evidence that the Pied Flycatcher density is negatively affected by the dominant Collared Flycatcher when that stronger species has a higher density. Clearly, both species fluctuated in a parallel way which contradicts an earlier generalization. The Pied Flycatcher breeds in Białowieża deciduous stands in much lower densities than the Collared Flycatcher does.
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