Abstract
Abstract. By providing nest boxes, previous studies have shown that nest sites are in short supply and limit the populations of several small passerines, including the Great Tit Parus major, the Blue Tit P. caeruleus, and the Pied Flycatcher Ficedula hypoleuca. Can this influence their distribution over a range of small woodland patch sizes in a heterogeneous landscape? To investigate this, a study was conducted in a heterogeneous agricultural landscape, with a mixture of wooded patches and cropped fields, in southern Sweden. The descriptive part of the study involved mapping territories of the three species in 135 patches. These species avoided small (<1 ha, Pied Flycatcher) or very small (<0.2 ha, the two tit species) forest patches in this landscape. In an experimental part, a subset of 34 patches, 0.01 to 24 ha in size was used. Territories were mapped in a first year as a control. In a second year, patches were matched by size and vegetation and nest-boxes were provided in one patch of each pair. Territories were again mapped. Providing nestboxes increased the density of breeding Great Tits in patches of all sizes and expanded their use of very small patches. The nest-boxes increased the density of Pied Flycatchers in large patches but not in small patches. So, is the lack of territories in small patches due to shortage of nest sites? The outcome of the experiment suggests nest site limitation as a cause of the observed Great Tit discrimination against very small habitat patches. The lack of Pied Flycatchers in small patches must however have another basis than lack of nest sites. The effect of providing nest-boxes on Blue Tit distribution was inconclusive.
Highlights
By providing nest boxes, previous studies have shown that nest sites are in short supply and limit the populations of several small passerines, including the Great Tit Parus major, the Blue Tit P. caeruleus, and the Pied Flycatcher Ficedula hypoleuca
Small forest patches may have a different set of tree species represented, compared to what is found in a natural climax forest
Holenesting birds may be limited by the availability of nest sites (Brawn and Balda 1988, Newton 1994, Bock and Fleck 1995, Thompson et al 2002) and it may be that differences in tree species composition and tree conditions cause nest sites for hole nesters to be in short supply in small habitat patches
Summary
Birds observed (seen or heard) were scored on a map and the number of territories evaluated from these locations The evaluation was based on clusters of locations and interpretation of behaviour like singing and territory disputes. All patches used by the present study species were wooded (but in the case of the smallest ones it sometimes happened by only one tree). This was part of a larger study reported by Loman and von Schantz (1991), where a fuller account of methods and study patches is given
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