Forest birds in forest fragments: are fragmentation effects independent ofseason?

The aim of this study was to examine whether effects of habitat fragmentati on on forest birds persist across seasons. We noted the presence or absence of 18 bird species in 16 wood plots on 12 occasions (six in winter and six in spring). Woodland area ranged between 0.5 and 200 ha. All patches consi sted of mature deciduous woodland. Degree of fragmentation for each woodlan d patch was indexed by the factor scores on the first two axes resulting fr om a principal component analysis, performed on a number of area and isolat ion variables. Both in winter and in spring, species richness correlated ne gatively with degree of fragmentation. The number of species observed was h igher in winter than in spring for most patches, but the difference was unr elated to the degree of fragmentation. On a species level, little evidence was found for an effect of interaction between season and degree of fragmen tation on the frequency of occurrence. The effects of fragmentation seem to depend on season in the Great Spotted Woodpecker Dendrocopos major and the Treecreeper Certhia brachydactyla, but not in the other species considered . Fragmentation has a negative effect on the frequency of occurrence of the Nuthatch Sitta europaea, Goldcrest Regulus regulus, Treecreeper, Great Spo tted Woodpecker and the Starling Sturnus vulgaris, and a positive effect fo r the Chaffinch Fringilla coelebs and, possibly, the Lesser Spotted Woodpec ker Dendrocopos minor. Seasonal changes in frequency of occurrence were not ed in four Of the species considered.