The Guadalupe Storm-Petrel was described in 1887, it was said to be an abundant breeder on Guadalupe Island, Mexico in 1906, and the last records of birds on Guadalupe come from 1912. It then disappeared and has not been seen again! Some consider the species extinct, while other hold out hope that it still exists. Predation by introduced rats, and habitat alteration by introduced goats are thought to be the culprits in the demise of the species. However, other storm-petrels have survived on the island, so perhaps another factor was involved? There is nothing known about the at-sea distribution of this storm-petrel. It was large and dark, with a white rump. It is thought to have been closely related to the Leach’s Storm-Petrel (Oceanodroma leucorhoa) complex, and although larger than the Leach’s it would be very difficult to separate from it without detailed study. The Guadalupe Storm-Petrel processed a broader and thicker bill, and apparently paler underwings than white-rumped Leach’s Storm-Petrels.