Two subspecies of the Wedge-rumped Storm-Petrel (Oceanodroma tethys) have been recognized, one that breeds on the Galapagos Islands (O. t. tethys) and a second that breeds on islands off the coast of Peru and Chile (O. t. kelsalli). We report a breeding colony of Wedge-rumped Storm-Petrels (O. t. kelsalli) on Ferrol Island, Peru. We observed 176 nests on 1-2 May 2006, including 55 (31%) with nestlings and 87 (50%) with eggs. Assuming an incubation period of 40-50 d, the first eggs would have been laid in mid-March. We found that O. t. kelsalli returned to land over a period of several hours at night. In contrast, O. t. tethys, the Galápagos subspecies, is apparently diurnal, with maximum activity during the midmorning hours. This difference in behavior may permit the exploitation of different food resources. The Peruvian government has not listed the Wedge-rumped Storm Petrel as a threatened species because of a lack of information about its population status. However, our observations suggest that Ferrol Island is an important breeding area for this storm-petrel. ©2007 Association of Field Ornithologists.