Leach’s Storm-Petrel (Oceanodroma leucorhoa) is a widespread bird of the North Pacific and North Atlantic oceans; in the former it breeds south to islands off western Mexico (AOU 1998). Four populations, differing mainly in the color of the rump, have been identified in western Mexico, breeding on Los Coronados (variably white rump), islets off Guadalupe Island in both summer and winter (white rump), and the San Benito Islands (dark-rumped). Furthermore, nonbreeding migrants, possibly from much farther north, occur south in the Pacific Ocean to about 15°S, mainly over offshore waters.