Preliminary Report Eastern Area Cruise Number 40 Coronado Islands Itinerary: 1040 - 1 May 1968 Land on North Island, Coronados Islands. 1400 -1530 - 1 May 1968 Survey Center Island from raft. 0800 - 2 May 1968 Depart North Island. During the period 1-2 May 1968 Robert DeLong and Richard Crossin surveyed North Island in the Coronados Islands offshore Baja California, Mexico. A brief run with a raft was made about the two islets comprising Center Island,but no landing was made. The following day we were transported to the islands and picked up by the charter vessel SIOUX CITY. The west and south sides of North Island were surveyed by raft, and seals and sea birds were recorded. All other pertinent data are included in the accounts below. Unless otherwise stated, all discussion concerns data collected on North Island. SPECIES ACCOUNTS Oceanodroma melania Black Petrel An unsuccessful preliminary search was made during daylight hours for this species. After observing the nestsites at night, it is doubtful if we would have detected the birds during the daytime if they had been there. Exactly at full dark,birds began flying in over the island and calls would soon be heard from all directions. The appearance of the storm petrels was exactly coincident with termination of Western Gull movements. This flight timing of the storm petrels has likely evolved in direct response to the movements of the predatory gulls. In the Central Pacific the White-throated Storm Petrel (Nesofregetta albigularis), with no resident predators, begins flying over the nesting islands in early evening, long before full dark. Flight activity in the Black Petrel was most intense during the first few hours after dark and essentially stopped by 2400 hours. DeLong noted an increase in flying birds near the water's edge at about 0100, perhaps of birds departing the island. Two characteristic calls are given by the birds. One is rather musical and given primarily in flight as the birds presumably trace back and forth over the nestsites. Occasionally this call may be uttered by a bird within the nest cavity. The other call, which is a variable "twitter", is apparently only given from the nest chamber. This latter call may be continuous for many minutes. Tape recordings of both calls were made.