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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.
Feeding habits of three sympatric owl species in a coastal woodland of central Italy (Migliarino-S. Rossore, province of Pisa) were investigated by using the pellet analysis method. The prey availability in the field was also investigated by means of two live-trapping sessions carried out in three different habitats. S. aluco preyed almost entirely upon medium and large sized rodents, and the size of its mean prey was significantly higher than that of A. otus and T. alba. The diets of A. otus and T. alba appeared quite similar, but the former was highly specialised in preying upon small rodents, whereas the latter fed upon shrews as well as rodents. Live-trapping sessions showed that Microtus savii was the prey species most abundant in the open areas, while Apodemus sp. — in the wooded and bushy ecotonal areas. Principal component analysis suggesting that A. otus was more linked to open fields as foraging habitat, while diet of T. alba was more similar to small mammal assemblages in ecotonal areas. The diet of S. aluco was not associated with any given habitat, probably because its favourite prey (Rattus rattus) is a semi- arboreal rodent.
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