Persistence and vulnerability of island endemic birds.

Abstract

This thesis investigates the dynamic relationship between the processes of extinction on islands and the traits of oceanic island endemic birds associated with persistence and vulnerability. This is explored using the comparative method and a data set of all birds endemic to oceanic islands. Two case studies are then presented to examine the resilience of the island endemic birds of Principe and Boné de Joquei in the Gulf of Guinea. When comparing closely related oceanic island and mainland birds, clutch size is lower on islands and, within islands it continues to decline as the distribution area of a species decreases. Small birds (<27 cm in body length) tend to get larger, and there is a trend for sexual size dimorphism to increase on oceanic islands. Recent extinction rates are lower on islands that have been exposed to humans for a long period of time. The birds on such islands are also less threatened by the introduction of exotics. A long period of exposure to humans also reduces the probability that the remaining species are flightless, ground-nesting, or non-forest- restricted endemics. When comparing island and mainland species that have similar areas of distribution, there is no significant difference in extinction risk. However, island birds are more threatened by introduced species. On oceanic islands, flightless birds, ground-nesting birds, birds with larger body size, and habitat specialists are associated with a greater risk of extinction than other birds. Sexually selected traits such as sexual body size dimorphism and dichromatism are not associated with elevated extinction risk. The resilience of the island endemic birds on Principe appears to be associated with a unique land use history and evolutionary exposure to predators, competitors and disease. Finally, a state of super abundance may be essential for the long-term persistence of endemic birds on small remote oceanic islands.Open acces