Explanations for bird species range size: ecological correlates and phylogenetic effects in the Canary Islands

Aim To explore the determinants of island occupancy of 48 terrestrial bird species in an oceanic archipelago, accounting for ecological components while controlling for phylogenetic effects. Location The seven main islands of the Canary archipelago. Methods We obtained field data on density, habitat breadth and landscape distribution in Tenerife, Fuerteventura and La Palma, trying to sample the whole availability of habitats and the gradient of altitudes. In total 1,715 line transects of 0.5 km were carried out during the breeding season. We also reviewed the literature for data on occupancy, the distance between the Canary Islands and the nearest distribution border in the mainland, body size and endemicity of the 48 terrestrial bird species studied. Phylogenetic eigenvector regression was used to quantify (and to control for) the amount of phylogenetic signal. Results The two measurements of occupancy (number of occupied islands or 10x10 km UTM squares) were tightly correlated and produced very similar results. The occupancy of the terrestrial birds of the Canary Islands during the breeding season had a very low phylogenetic effect. Species with broader habitat breadth, more intense preferences for urban environments, smaller body size, and lower degree of endemicity had a broader geographical distribution in the archipelago, occupying a larger number of different islands and 10x10 UTM squares. Main conclusions The habitat generalist species with a tolerance for novel urban environments tend to be present in more islands and to occupy more area, while largesized species that are genetically differentiated within the islands are less widespread. Therefore, some properties of the ranges of these species are explicable from basic biological features. The positive relationship with local abundance, previously uncovered in continental studies, was not found, probably because it relies on free dispersal on continuous landmasses that may be short-circuited in oceanic island scenarios.