Alijos Rocks (24°57'N, 115°45'W) lie 185 nautical miles almost due west of Cabo San Lazaro, off southwestern Baja California, Mexico (Figures 1–5). Their jagged, volcanic spires consist of three main stacks and numerous smaller rocks. South Rock, the largest of the group, rises 34 m above the sea; North Rock is 22 m high and Middle Rock, the smallest, is approximately 18 m high. The total top surface area of the three main pinnacles is under ¼ acre (0.1 hectare).
The only published accounts of biological surveys of Alijos Rocks come from Hanna (1926) and McLellan (1926), who spent 3 hours rowing among the rocks on 24 April 1925, and Murphy (1958) who visited the area on 9 November 1956. Since 1974 I have passed by these pinnacles five times recording bird and mammal observations while aboard research vessels. A list of survey dates and pertinent comments is given in Table 1. In addition, Bayard Brattstrom visited Alijos Rocks on 10 May and 15 November 1953, and David Au surveyed them on 7 December 1976 by helicopter from a passing research vessel.