EUROPEAN NUTHATCH METAPOPULATIONS IN A FRAGMENTED AGRICULTURAL LANDSCAPE

The European nuthatch Sitta europaea, which inhabits mature deciduous and mixed forest, has a fragmented distribution in the agricultural landscapes of Western Europe. Nuthatches have a high site fidelity, which makes them potentially sensitive to fragmentation. In earlier studies patch area and isolation were found to be related to nuthatch distribution pattern. In this paper, three time series of occurrence data are analysed to assess the effects of patch size (carrying capacity), habitat quality and isolation on the processes of local extinction and colonization. The results are interpreted in terms of a modified Levins metapopulation model, with patches of unequal size and habitat quality and effects of inter-patch distance and configuration. A method is presented to estimate the parameters of this model. The nuthatch is found to show all the characteristics of a Levins type metapopulation: the distribution is dynamic in space and time. Furthermore, extinction rate depends on patch size and habitat quality and colonization rate on density of surrounding patches occupied by nuthatches.