NOORDEN B VAN, OPDAM P & SCHOTMAN A (1988) Density of forest interior birds in isolated wood lots. LIMOSA 61 (1): 19-25.

Evidence is accumulating suggesting that the distribution of a number of forest interior bird species in isolated forest patches is affected by area of the patch, interpatch distance, amount of forest nearby the patch, and the degree of connectivity by fencerows. We assume that such effects could also result in vacant territories in occupied wood lots and hypothesize that isolation parameters are also related to density. To test this hypothesis, we selected 46 mature deciduous wood lots, ranging is size between 0.1 and 31.5 ha, situated in an agricultural landscape in the centre of the Netherlands, sandwiched between two large forest areas (fig. I). Bird territories in these wood lots were accurately mapped. Also seven variables of forest structure and eight variables of isolation (app. 1) were measured in the field and from geographical maps. For analysis, we used multiple regression techniques. Only species restricted to mature deciduous forest were considered (tab. 1). Several isolation variables appeared to be correlated with total density and to the density of Great Spotted Woodpecker, Long-tailed Tit, Nuthatch, Short-toed Treecreeper, and Chaffinch (tab. 2, fig. 2). A negative effect of wood lot size was considered as a side-effect of calculating density on 10 ha basis. Two explanations are offered for this result. The hypothesis about an effect of distance on immigration and reoccupation of deserted territories is supported by the fact that, except for the Chaffinch, all species found to be affected in density had previously been found to be affected in distribution also (tab. 3). Furthermore, indications are discussed supporting the hypothesis that nearby wood lots and fencerows may serve as a feeding habitat, particularly outside the breeding season. We conclude that both hypotheses, which are not conflicting with each other, are plausible and worthwhile to test in future research. ##### European Green Woodpecker Picus viridis Black Woodpecker Dryocopus martius Great Spotted Woodpecker Dendrocopos major Lesser Spotted Woodpecker Dendrocopos minor Common Redstart Phoenicurus phoenicurus Spotted Flycatcher Muscicapa striata European Pied Flycatcher Ficedula hypoleuca Long-tailed Tit Aegithalos caudatus Marsh Tit Poecile palustris Willow Tit Poecile montanus Blue Tit Cyanistes caeruleus Eurasian Nuthatch Sitta europaea Short-toed Treecreeper Certhia brachydactyla Eurasian Golden Oriole Oriolus oriolus Common Chaffinch Fringilla coelebs

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