Ecological Correlates of Residence and Non-Residence in a Mediterranean Passerine Bird Community

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Abstract
A southern Spanish passerine bird community was studied throughout a year, collecting information on species composition and abundance, foraging behaviour and feeding site utilization of component species. Comparisons of behavioral, morphological and feeding site niche characteristics between resident and non-resident species are made. For all species, within-species foraging diversity is significantly greater for non-resident than for resident species. Resident species are morphologically more diversified and less densely packed in the morphological space than non-resident ones. Resident species tend to show a wider range of bill length and to be long-billed with respect to non-residents. Resident species exhibited feeding site niche shifts in response to its own population density, higher densities promoting wider niches as theoretically expected. Non-residents did not show comparable shifts, although some degree of response to density was noted. A canonical correlation analysis showed that resident and non-resident species adjust themselves to the changing environment in different ways. The seasonal organization of the study community is discussed in relation to other temperate and non-temperate communities. The observed great dominance of residents with respect to number of individuals may be associated with a relatively low degree of seasonality in food supply to birds.