Avifauna of the Revillagigedo Islands
In April 1978, a Carnegie Museum of Natural History/Hubbs-Sea World Research Institute expedition visited Socorro and San Benedicto islands, which are located between 370 and 400 km (230-250 miles) south of the tip of Baja California. Our purpose was to determine the status of the endemic birdlife, and to obtain anatomical material and sound recordings, which had not been available previously, for taxonomic studies. A second expedition, in April 1981, was directed at clarifying the status of several species in light of our earlier findings.
This paper summarizes the status of birds on islas Socorro and San Benedicto based largely upon visits in April 1978 and April 1981, and presents additional data on Isla Clarion. Isla Socorro is in a state of change, seemingly as a result of increased human activities since 1958 and the consequent introduction of domestic animals. Nine endemic avian taxa have been described for Socorro. In the past two decades, several of these have shown sharp declines which seem largely attributable to predation by domestic cats. Pipilo erythrophthalmas socorroensis seems far less common than in the recent past. Mimodes graysoni, once described as the most common landbird on Socorro, is extremely rare and local and its condition seems precarious. Zenaida graysoni is apparently extinct. Thryomanes sissonii, Aratinga holochlora brevipes, Columbina passerina socorroensis and Parula pitiayumi graysoni remain common; indeed the warbler may have increased. We are unable to present any new data for Nyctanassa violacea gravirostris or Micrathene whitneyi graysoni. Two species have invaded Socorro. Zenaida macrowa became well established between 1971 and 1978 and Mimus polyglottos between 1978 and 1981. Resident landbirds are absent from San Benedict0 but seabird numbers have increased since the eruption of Volcan Barcena in 1952. Notes on 25 species recorded for the first time are included.