Townsend's Storm-Petrel shares with Ainley's Storm-Petrel (Oceanodroma cheimomnestes) a very restricted breeding distribution: both species nest only on a few islets at the southern end of Guadalupe Island, off of the northwestern coast of Mexico. Although these two species share the same islets, they scarcely overlap, as each breeds at a different time of year. Townsend's occupies the site in the warmer months, with egg laying from late May to the end of June, and the nestlings fledge in late September and early October. In contrast, egg-laying by Ainley's Storm-Petrel is believed to occur from mid-November through December, with most nestlings fledging from early March through to mid-April. In addition to this temporal segregation, Ainley's and Townsend's storm-petrels have different vocalizations, and also have subtle size and plumage differences. Very little is known about the nonbreeding distributions of these species, due to their similarity to each other and to Leach's Storm-Petrel (Oceanodroma leucorhoa), and to the rarity of both species, but Townsend's Storm-Petrel disperses both north and south at sea, extending from the waters off of southern California, United States, and at least to a latitude of 10º N.