HABITAT DISTRIBUTION OF CANARY CHAFFINCHES AMONG ISLANDS - COMPETITIVE-EXCLUSION OR SPECIES-SPECIFIC HABITAT PREFERENCES

The habitat distribution between islands of the Common Chaffinch (Fringilla coelebs L.), viewed in relation to the presence of its potential competitor species, the Blue Chaffinch (Fringilla teydea Moquin-Tandon), has been studied for the Canary Islands (Tenerife and El Hierro). The Common Chaffinch was significantly denser in the pine woods of El Hierro than in Tenerife, while the Blue Chaffinch was only present in Tenerife. The vegetation structure was very different in the pine woods of the two islands. In the pine woods of El Hierro, the Common Chaffinch selected more grassy places, and foraged mainly in the foliage. The habitat selection pattern observed in Hierro was congruent with that obtained for the continental subspecies in the North of the Iberian Peninsula. An empirical model was thus developed to predict density variations of the Common Chaffinch in the continental pine woods of Northern Spain. This continental model (not subject to the influence of the potential competitive effect of the Blue Chaffinch) was then used to predict the abundance of the Common Chaffinch in the pine woods of El Hierro and Tenerife. The similarity between the densities predicted by the non-competitive continental model and those actually observed in the pine woods of El Hierro and Tenerife indicates that the presence of the Blue Chaffinch is not relevant in explaining the differences in Common Chaffinch density between islands. The habitat preferences of the Common Chaffinch quantitatively explain density differences observed between El Hierro and Tenerife. These results show clearly the relevance of habitat structure in determining the patterns of presence and density of the Common Chaffinch between islands. Data obtained thus supports the species-specific habitat preference hypothesis, with the competitive exclusion hypothesis not being justified at least in ecological time.