Wintering avifauna in the agricultural landscapes of northern Spain. II. The role of habitat structure and interspecific competition
Published: Volume 32(2), December 1985. Pages 227-251.
Original Title: Avifauna invernante en los medios agrícolas del norte de España. 2. Papel de la estructura de la vegetación y la competencia interespecífica.
This paper deals with the composition and structure of the wintering bird community in the agricultural areas of the Atlantic Basque Country and the habitat preferences of the species. To study this, 455 samples (0,2 ha) of the vegetation structure of the space occupied by 27 species have been taken (point centered count method of NOON, 1981a). Using the Principal Component Analysis (PCA) and considering weighted average data for each species (see Apendix), it has been found that the spatial niche is determined by 3 significant factors (table 1): structural complexity gradient (PCI), agricultural exploitation of the soil (PC2) and maturity of the hedges (PC3) (see figures 1 and 2 for the position of species in relation with these factors). Species abundance has no relation with habitat-width (table II). The relation between dominance and habitat-width proposed by McNAUGHTON and WOLF (1970) was not supported by our data. The strong interspecific overlap on PC1 and PC2 (especially among strictly wintering species), the lack of complementarity among the components of spatial niche and the fact that congeneric and morphologically very similar species do not overlap less than expected by chance (table III), suggest that competition does not determine the distribution of species. As a consequence of environment instability and adversity, outside and inside the area considered, the community is not saturated either for species or individuals. All these facts indicate that the bird communitty is not in equilibrium (in the sense of WIENS, 1984) and that its composition and structure is the result of species-specific habitat preferences. Correlating the position of species in a regional structural factor (F2 in TELLERIA and SANTOS, 1985) with their position on PC1 and PC2, it has been observed that local habitat preferences explain fairly well the regional distribution pattern (see figure 7).