Ecological basis of extinction risk in birds: Habitat loss versus human persecution and introduced predators

Understanding the ecological mechanisms that underlie extinction is fundame ntal to conservation. It is well established that not all taxa are equally vulnerable to extinction, but the reasons for these differences are poorly understood. This may be, in part, because different taxa are threatened by different mechanisms. Theoretically, sources of extinction risk that pertur b the balance between fecundity and longevity, such as human persecution an d introduced predators, should be particularly hazardous for taxa that have slow rates of population growth. In contrast, sources of extinction risk t hat reduce niche availability, such as habitat loss, should represent a par ticular threat to taxa that are ecologically specialized. Here we test thes e predictions by using a phylogenetic comparative method and a database on 95 families of birds. As theory predicts, extinction risk incurred through persecution and introduced predators is associated with large body size and long generation time but is not associated with degree of specialization, whereas extinction risk incurred through habitat loss is associated with ha bitat specialization and small body size but not with generation time. Thes e results demonstrate the importance of considering separately the multiple mechanisms that underlie contemporary patterns of extinction. They also re veal why it has previously proven so difficult to identify simple ecologica l correlates of overall extinction risk.