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The nuthatch, Sitta europaea L., is a small (23 g), cavity-nesting woodland bird which, since the 1970s, has been expanding its range in Britain. However, within this range, the species is notably scarce in an area of eastern England. This gap in the species distribution could arise for several reasons including habitat quality, local landscape structure, regional landscape structure and climate. Field surveys and logistic models of breeding nuthatch presence/absence were used to investigate the relative influences of habitat quality, landscape structure and climate on the prevalence of nuthatches in eastern England. Field surveys of woods in the study area indicated that habitat quality was sufficient to support a nuthatch population. A model of habitat occupancy in relation to local landscape structure, developed in the Netherlands, was applied to the study area. The number of breeding pairs predicted for the study area by the model was lower than expected from habitat area alone, suggesting an additional effect of isolation. However, observed numbers were even lower than those predicted by the model. To evaluate the possible roles of climate and large-scale landscape structure on distribution, presence/absence data of breeding nuthatches at the 10-km grid square scale were related to variables describing climate and the amount and dispersion of broadleaved woodland. While climate in the study area appeared suitable, models including landscape variables suggested that the study area as a whole was unlikely to support nuthatches. Although suitable habitat was available, woodland in the study area appeared to be too isolated from surrounding nuthatch populations for colonisation to be successful. This situation may change if current increases in both national and regional populations continue, thus increasing the number of potential colonists reaching the study area.

In The Netherlands, fragmentation of (semi)natural ecosystems is regarded as a major nature conservation problem. The current Dutch Nature Conservation Policy Plan proposes a spatial network consisting of existing nature reserves, nature redevelopment areas and corridor zones. One of the objectives is to stop the assumed decline of biodiversity due to fragmentation. In this contribution we show that breeding birds are affected by the spatial distribution of their habitat. We also show how problems due to fragmentation can be solved by integrating landscape ecological research data into planning procedures. Fragmented bird populations show metapopulation characteristics, dependent on the degree of fragmentation. This can be concluded from pattern studies, in which presence or absence patterns are correlated with spatial characteristics. Metapopulation dynamics were used, and the frequency of local extinction and of recolonization were related to size of habitat patches and spatial position in the landscape. The conclusion is that, depending on the spatial scale, landscape fragmentation is a threat to birds. On the basis of empirical data, statistical and metapopulation models are being developed to be used to evaluate spatial planning scenarios and to support decision making about which scenario is closest to the planning aims.

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