. Bulletin. Science; Natural history; Natural history. 94 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Photograph 2. Nest on a beached trawler as seen from the air north of Puertocitos. It is not difficult to note the tracks around the nest made by recreationists in all-terrain vehicles. A further complication concerns the presence of nonbreeding birds. One-year olds and many of the 2-yr olds are generally not present on the breeding grounds of the more northern migratory population in the United States (Henny and Van Velzen, 1972). An attempt was made to record these birds as singles during the s
. Bulletin. Science; Natural history; Natural history. 94 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Photograph 2. Nest on a beached trawler as seen from the air north of Puertocitos. It is not difficult to note the tracks around the nest made by recreationists in all-terrain vehicles. A further complication concerns the presence of nonbreeding birds. One-year olds and many of the 2-yr olds are generally not present on the breeding grounds of the more northern migratory population in the United States (Henny and Van Velzen, 1972). An attempt was made to record these birds as singles during the study; however, this was difficult where nesting was concentrated. Locations where apparent nonbreeding birds were concentrated will be discussed. Results Present Distribution and Abundance To facilitate presentation of the findings, we have divided the survey into seven regions: Northwest Baja California, Southwest Baja California, Northeast Baja California, Southeast Baja California, Midriff Islands, Coastal Sonora, and Coast- al Sinaloa. A minimum estimate of the total nesting population within the survey area was 810 ± 55 pairs (95% ). Northwest Baja California.—The area extends from the border south to and including Scammon's Lagoon, and west to Punta Eugenia, including Natividad and Cedros islands. The San Benitos Islands were not surveyed in 1977, although recent population data are provided. The total nesting population in the region is estimated at 138 pairs (Table 3). No nesting pairs were observed between the border and Desembarcadero de Santa Catarina. However, from this point south to Morro Santo Domingo, an estimated 20 pairs were nesting, pri- marily on cliffs, although one pair nested in a yucca {Yucca spp.). The nesting pairs associated with Scammon's Lagoon were concentrated on three small is- lands (27 pairs), plus towers, platforms, pilings, channel markers, and debris that drifted ashore near the mouth of the lagoon and at Estero de San Jo
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