extinct in the wild. Socorro is an important breeding location for several seabirds, many of which have here one of their north(east)ernmost breeding colonies. The present status of these birds is not well known, and they presumably have suffered from cat predation. In 1953, the following taxa were present: Wedge-tailed shearwater, Puffinus pacificus (or Ardenna pacifica) Western red-billed tropicbird, Phaethon aethereus mesonauta – breeding suspected but not verified Nazca booby, Sula granti – breeding suspected but not verified Northeast Pacific brown booby, Sula leucogaster brewsteri – breeding suspected but not verified East Pacific great frigatebird, Fregata minor ridgwayi – breeding suspected but not verified; a doubtfully distinct subspecies East Pacific sooty tern, Onychoprion fuscatus crissalis – a doubtfully distinct subspecies East Pacific brown noddy, Anous stolidus ridgwayi Non-endemic landbirds and shorebirds occur mostly as vagrants or use the island as a stopover during migration; the northern mockingbird became established in the late 20th century. Among those that are recorded not infrequently are great blue heron, Hudsonian curlew, spotted sandpiper and wandering tattler. Unlike the situation on smaller and more isolated Clarión, wind-blown or vagrant birds seem to constitute the bulk of the recorded species, including brown pelican, osprey, peregrine falcon, semipalmated plover, willet, sanderling, belted kingfisher and buff-bellied pipit. It may be that this puzzling observation is due to the presence of the red-tailed hawks and cats, which has at least made the local Urosaurus more wary than its relative on Clarión, and might deter passing birds from stopping on Socorro. Endemism Being the largest of the Revillagigedo Islands and closer to mainland than Clarion, Socorro sports a rich array of endemic taxa, mainly plants and landbirds as well as lizards. Some are threatened due to the presence of feral cats. Animals Socorro parakeet, Aratinga brevipes (endangered) Socorro red-tailed hawk, Buteo jamaicensis socorroensis Socorro common ground dove, Columbina passerina socorroensis Socorro elf owl, Micrathene whitneyi graysoni (probably extinct since c. 1970) Socorro mockingbird, Mimodes graysoni (critically endangered) Socorro yellow-crowned night heron, Nycticorax violaceus gravirostris (or Nyctanassa violacea gravirostris) Socorro tropical parula, Parula pitiayumi graysoni Socorro towhee, Pipilo (maculatus) socorroensis Townsend's shearwater, Puffinus auricularis (critically endangered; recently extirpated from San Benedicto and probably Clarión) Socorro wren, Troglodytes sissonii (near threatened) Socorro dove, Zenaida graysoni (extinct in the wild) Urosaurus auriculatus (endangered) Plants Acalypha umbrosa Aegopogon solisii Aristida vaginata Aristolochia socorroensis Bidens socorrensis Botrychium socorrense Castilleja socorrensis Cestrum pacificum Coreocarpus insularis Croton