The biogeography of avian extinctions on oceanic islands

Aim To test the influences of island area, island isolation, and human-introduced mammalian predators on avian extinctions that have occurred on oceanic islands worldwide. Location The oceanic islands of the world. Methods We augmented and re-examined an existing data set for 218 oceanic islands by means of causal modelling using path analysis (a form of structural equation modelling) and a null model. Results The number of extinctions was not a simple function of the number of bird species on the various islands. Whereas introduced mammalian predators had an influence on the number of extinctions, island area (via indirect influences) and isolation (via direct influences) were equally or more important. Main conclusions The multiple influences of physical and biotic factors on past extinctions can be revealed through modelling the causal influences of physical attributes of islands on biological characteristics, and the causal influences of both physical and biological characteristics on extinctions.