Causes of exotic bird establishment across oceanic islands

The probability that exotic species will successfully establish viable populations varies between regions, for reasons that are currently unknown. Here, we use data for exotic bird introductions to 41 oceanic islands and archipelagos around the globe to test five hypotheses for this variation: the effects of introduction effort, competition, predation, human disturbance and habitat diversity (island biogeography). Our analyses demonstrate the primary importance of introduction effort for avian establishment success across regions, in concordance with previous analyses within regions. However, they also reveal a strong negative interaction across regions between establishment success and predation; exotic birds are more likely to fail on islands with species-rich mammalian predator assemblages.