Revillagigedo Islands - Ecology

Ecology

The Revillagigedo Islands are home to many endemic plant and animal species, and are sometimes called Mexico's "little Galapagos". They are recognized as a distinct terrestrial ecoregion, part of the Neotropic ecozone. Socorro is the most diverse in flora, fauna, and topography. The Mexican Government established the islands as a Biosphere Reserve on June 4, 1994.

According to the WWF, 14 of the islands' 16 generally accepted resident taxa of landbirds as well as one seabird are endemic, as are all of the islands' native terrestrial vertebrates. The latter, however, consist only of one Masticophis whipsnake and two Urosaurus iguanids. Numerous seabird taxa breed no further north(east)wards than San Benedicto; storm-petrels are notably absent as breeders though they breed in the region and visit the islands to forage. Albatrosses are also not normally found here. Among landbirds, the absence of the House Finch, widespread on northeastern Pacific offshore islands, is the most conspicuous one.

Apart from the native birds, migrant shorebirds and others are often found on the islands. Bahia Azufre (Sulfur Bay) on Clarión seems to be a favorite stopover location, as it is one of the few longer stretches of beach in the islands; mostly, the shoreline is steep cliffs.

Socorro has numerous endemic plant taxa, whereas Clarión which is farthest from land has but a few. The San Benedicto was effectively wiped out in the devastating eruption of Bárcena volcano on August 1, 1952, but has since recovered; apparently just the San Benedicto Rock Wren became entirely extinct. Most if not all native plants found on San Benedicto today are shared with Clarión, not with the closer Socorro to the south, due to the prevailing winds and ocean currents. The native flora of Clarión is about equally shared with both other large islands.

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.