Assessing the ecological basis of conservation priority lists for bird species in an island scenario

Proneness to extinction varies naturally and continuously according to the ecological phenomena that compound rarity even before anthropogenic effects may play a role. This is particularly obvious in islands, where populations are often (and naturally) small and fragmented and, consequently, conservation priority lists may have a large number of species clustered unhelpfully in the higher threat categories. In this study we propose a simple model of threat based on natural descriptors of rarity and taxonomic distinctiveness (area of occupancy, population abundance and trend, and endemicity), assess its correlation with ecological features of the species (habitat preferences and body size) and check whether the Spanish Red data Book and a normative conservation priority list (the Canary Islands Catalogue of Threatened Species and its administrative revision) includes these ecological bases for birds. We found that a large variation in threat (48.2%) was explained by phylogeny, habitat breadth and preference for urban areas (with a negative effect), and preference for agricultural environments (a positive effect). The Spanish Red data Book and the administrative lists tested are poorly related to descriptors ordering the extinction risk and loss of taxonomic singularity, so some changes would make their categories more coherent. We contend that the ecological bases of rarity should be taken into account to understand why some populations/species are at higher extinction risk whereas others remain relatively safe, as this would provide firmer grounds on which to base conservation priorities.