Information on the seabirds of northwestern Mexico has accumulated for several decades now, but seabirds along the country’s southern Pacific coast remain little studied. Morros El Potosí (17° 31′ 57″ N, 101° 29′ 18″ W; known as “White Friars Rocks” in the American navigation literature) consist of three small islands and several rocks 3 km offshore and 15 km east of the city of Zihuatanejo, Guerrero (Figure 1). The main islands are 50–65 m high (Hydrographic Office 1937) and very steep, with vertical cliffs that rise from their faces.