As opposed to the interchange between the islands, the animals and plants that colonized them initially are apparently all from mainland populations generally to the northeastward of the Revillagigedos. Plants are most often derived from Baja California founder populations, whereas the endemic nonavian reptiles seem to be rather derived directly from mainland populations of the Sonora-Sinaloa area. The ancestors of the islands' terrestrial birds probably came from the general area of southern North and northern Central America. As illustrated by the fact that no endemic landbird taxon occurs on more than one island and the cases of the Socorro and Clarión wrens as well as the Socorro dove and Clarión mourning dove, each bird population seems to have arisen independently. The archipelago has been recognised as an Important Bird Area (IBA) by BirdLife International for its breeding seabirds and endemic landbirds.
