Wilson’s Storm-Petrel Oceanites oceanicus
Breeding in the Antarctic and subantarctic, Wilson’s Storm-Petrel migrates in large numbers to the North Atlantic but in only small numbers to the North Pacific. In California, it is seen annually in Monterey Bay and over Cordell Bank near Point Reyes but rarely elsewhere. There are just five sightings within 45 miles of San Diego County’s coast.
Migration: San Diego County’s records of Wilson’s Storm-Petrel are all for August and September: 25 miles west-northwest of Point Loma 31 August 1935 (Miller 1936, UCLA 2222), 6 miles west of Point Loma 3 September 1980 (D. W. Povey, Roberson 1993), 25 miles west of Point Loma 28 August 1988 (G. McCaskie, Pyle and McCaskie 1992), 30 miles west of Point Loma 10 September 1988 (same individual as last?, W. Russell, Patten and Erickson 1994), and 45 miles off San Diego 8 September 1996 (G. McCaskie, NASFN 51:119, 1997).
Taxonomy: Wilson’s Storm-Petrel is commonly divided into two subspecies, longer-winged O. o. exasperatus Mathews, 1912, nesting around Antarctica and nominate O. o. oceanicus (Kuhl, 1820), nesting on subantarctic islands. The single specimen from San Diego County (UCLA 2222) needs to be reexamined for determination of its subspecies.
Fork‑tailed Storm-Petrel Oceanodroma furcata
The Fork-tailed is the most boreal storm-petrel in the North Pacific, most abundant in Alaska and breeding south only to Humboldt County, California. The 13 records from San Diego County are the southernmost well-supported occurrences along the Pacific coast, though the species has been recorded in Hawaii as well.
Winter: The Fork-tailed Storm-Petrel is sporadic at the southern tip of its range, with occurrences clumped in small irruptions. In 1990, one was picked up on the beach at La Jolla (P7) 14 February 1990 (SDNHM 46392) and two were seen from shore there 19 February (G. McCaskie, AB 44:327, 1990). The only other December–February record is of one found dead at Ocean Beach (R7) 23 December 1918 (Stephens 1919b, SDNHM 2031).
Migration: Most records of the Fork-tailed Storm-Petrel for San Diego County are for spring rather than winter. The total spread of dates is from 9 September (1990, one photographed off San Diego, J. O’Brien, AB 45:150, 1991) to 9 June (1939, one found exhausted on the beach at Cardiff, L7, Huey 1939, SDNHM 18075). Other records more recent than the five listed by Unitt (1984) are of up to seven seen from shore at La Jolla 13–23 April 1995 (S. Walens, NASFN 49:308, 1995) and birds found dead and partly decomposed by Brian Foster at the mouth of Aliso Creek, Camp Pendleton (F4) 1 May 1999 (SDNHM 50279) and 4 April 2001 (SDNHM 50867) and on the Silver Strand, Coronado (T9) 19 May 1997 (SDNHM 49806) and 7 May 1999 (SDNHM 50278).
Taxonomy: The Fork-tailed Storm-Petrel is generally divided into two subspecies, paler more northern nominate O. f. furcata (Gmelin, 1789) and darker, more southern O. f. plumbea (Peale, 1848), including the specimens from San Diego County. Boersma and Silva (2001) suggested that the validity of the distinction needs reevaluation.
Leach's
Storm-Petrel Oceanodroma
leucorhoa
Of the storm-petrels of the North Pacific Ocean, Leach’s has the widest range, in both dispersion of breeding colonies and dispersion of nonbreeding birds at sea—Leach’s occurs even in the most remote parts of the North Pacific, in areas where there are few if any other birds. Off San Diego County, Leach’s occurs farther offshore than the other species and is rarely seen by day within 25 miles of land. Yet Los Coronados Islands, within sight of San Diego, are the site of a colony, a population showing the full spectrum of the species’ variation from white rumped to dark rumped.
Migration: Leach’s Storm-Petrel occurs off southern California year round but is common only from June to October, during the species’ breeding season. From December to May numbers are low (Briggs et al. 1987). Leach’s is less gregarious at sea than the Black or Least Storm-Petrels, so the maximum counts per day are less (up to 400 near San Clemente Island 1 September 1958, AFN 13:62, 1959), though Briggs et al. (1987) observed in August 1977 a density of 2.6 birds per square kilometer.
Four Leach’s Storm-Petrels found in San Diego Bay have been brought to wildlife rehabilitators but died and are preserved as specimens. Their dates range from 23 July to 1 October, the time when young are fledging from the colony on Los Coronados Islands. Possibly the birds were disoriented by the lights of Tijuana and San Diego and flew toward shore, or, at night, they crashed onto boats that later came back to port at San Diego. One picked up in El Cajon (Q13) 19 September 1988 was fatally disoriented (AB 43:538, 1989, SDNHM 45435).
Winter: One seen from shore at La Jolla (P7) 14 December 1995 (S. Walens, G. McCaskie, NASFN 50:220, 1996) provided the only specific winter record of Leach’s Storm-Petrel near the coast of San Diego County.
Taxonomy: The classification of Leach’s Storm-Petrel into subspecies is unsatisfactory. The highly variable population on Los Coronados Islands could be considered intergrades between the white-rumped O. l. leucorhoa (Vieillot, 1818) and the dark-rumped O. l. chapmani Berlepsch, 1906. Bourne and Jehl (1982) and Power and Ainley (1986) placed it with chapmani. Few white-rumped specimens collected away from nesting colonies can be identified as the larger O. l. leucorhoa versus the smaller O. l. socorroensis Townsend, 1890. The measurements tabulated by Huntington et al. (1996) suggest the degree of overlap in size may be too much for long-recognized distinction between these two subspecies to be maintained.
Ashy Storm-Petrel Oceanodroma homochroa
The Ashy Storm-Petrel is almost endemic to California. The small, possibly ephemeral colony on Los Coronados Islands is the only one south of the Mexican border. San Diego County is thus marginal to the Ashy Storm-Petrel’s range, and the species appears rare in the county’s offshore waters—though the difficulty in identifying it in the field undoubtedly means some are overlooked.
Migration: The Ashy Storm-Petrel is not strongly migratory; it remains year round in the California Current. On the ocean near the coast of San Diego County the species is rare, usually seen singly if at all. A count of 40 off San Diego 4 December 1966 (G. McCaskie) remains the highest. The Ashy Storm-Petrel is most frequent in fall and winter, with dates ranging from 25 July (1964, G. McCaskie) to 19 May (1973, AB 37:819, 1973; 1979, AB 33:805, 1979).
Surprisingly, the Ashy Storm-Petrel has been picked up within San Diego Bay or on land within the city of San Diego on several occasions, all between 6 September (found on the grounds of the San Diego Zoo, R9, SDNHM 30301) and 22 November (1981, found in an airplane hangar at Lindbergh Field, S9, SDNHM 41597). Unitt (1984) listed four such records; more recent were one in National City (T10) 30 September 1995 (SDNHM 49486), one found in the trolley yard in downtown San Diego (S9) 25 September 2000 (SDNHM 50480), and one caught by a cat along Illinois Street near El Cajon Boulevard in the North Park area of San Diego (R10) 10 September 2002 (SDNHM 50664). The last was over 6 miles inland from the beach at Coronado. The coinciding of these onshore records in the fall with those of the Black and Leach’s Storm-Petrels suggests that in all three species young fledging at night from the colony on Los Coronados Island became disoriented by city lights. Yet the population of the Ashy on Los Coronados is thought to be very small, much smaller than that of the other two species. Jehl (in Jehl and Everett 1985) suggested only two or three pairs, though Everett and Anderson (1991) thought it could be greater.
Conservation: The total population of the Ashy is much less than that of the other North Pacific storm-petrels, probably under 10,000. Increasing populations of Western Gulls nesting at the same sites, especially Southeast Farallon Island, could threaten it (Ainley 1995). On Los Coronados Islands the main threat has been the release of cats and rats. Much of the storm-petrel’s population congregates in fall on Monterey Bay, another bottleneck of vulnerability.
Black Storm-Petrel Oceanodroma melania
The Black is the most numerous of the storm-petrels occurring on the ocean off San Diego County and nests on Los Coronados Islands. It is primarily a summer visitor, regular just two or three miles off shore but rarely seen from land. On several occasions disoriented young Black Storm-Petrels have been picked up inland in metropolitan San Diego.
Migration: The Black Storm-Petrel is seen off San Diego County mainly from April to November, corresponding to the time at which the birds are at the colony on Los Coronados Islands. At times, however, many more birds are seen off San Diego (up to 2000 on 17 September 1970, AB 32:107, 1971; 1300 on 13 September 1992, AB 47:148, 1993) than can be accounted for by the local population (estimated at 100 pairs on Middle Rock of Los Coronados Islands 1989–90, Everett 1991). The Black Storm-Petrel’s migration reflects that of many seabirds nesting primarily around Baja California, with movement north in summer after breeding, then movement south in winter (Everett and Ainley 2001). Briggs et al. (1987) found the species reaching its peak numbers off southern California in August and September, within 50 km of the mainland coast.
Perhaps because it largely vacates the ocean off San Diego during the season of winter storms, the Black Storm-Petrel is rarely seen from shore. It has been noted, however, from San Onofre (C1; one on 21 June 1997, L. Ellis), La Jolla (P7; e.g., one 19–23 April 1995 (S. Walens, NASFN 49:308, 1995), and Point Loma (S7; one on 24 November 1983 (R. E. Webster, AB 38:246, 1984). One sighting has been reported from south San Diego Bay (U10), 15 September 2000 (J. L. Coatsworth, NAB 55:102, 2001).
Black Storm-Petrels have been picked up within urban areas and brought to wildlife rehabilitators from intersection of 30th Street and El Cajon Boulevard (R10) 10 September 2002 (SDNHM 50687), the 32nd Street naval station (S10) 21 September 2001 (SDNHM 50614), Balboa Park (R9) 22 September 2000 (SDNHM 50481), near 19th and Market streets in downtown San Diego (S9) 22 October 1998 (SDNHM 50173), and along Woodside Avenue, Lakeside (P13), 11 November 2000 (SDNHM 50497). At about 18 miles from the coast, the last locality is the farthest inland. The convergence of all these dates in the fall suggests that the birds became disoriented as they fledged from Los Coronados Islands, an idea reinforced by the downy feather tips still adhering to the bellies of the specimens from Balboa Park and the 32nd Street naval station.
Winter: The only specific reports of the Black Storm-Petrel from or near San Diego County December–March are of one on the San Diego Christmas bird count 2 January 1961, one on the Rancho Santa Fe Christmas bird count 16 December 1984, four on the latter count 28 December 1996, five off San Diego 18 January 1969 (AFN 23:519, 1969), and five off San Diego 21 January 1984 (G. McCaskie, AB 38:357, 1984). Briggs et al. (1987) reported the Black Storm-Petrel off southern California in all months but identified only a few in winter. Because of the difficulty in distinguishing all-dark storm-petrels in the field, unseasonal sightings, including those listed here, must be regarded with caution.
Conservation: Though still abundant, the Black Storm-Petrel is vulnerable because the overwhelming majority of the population nests in a small area, the three San Benito Islands off the Pacific coast of central Baja California. On all its nesting islands, including Los Coronados, the primary threat to the Black Storm-Petrel has been the introduction of mammals: cats, rats, dogs, and pigs. Though some of these predators have been eradicated from some islands, thanks mainly to the efforts of Island Conservation in cooperation with Mexico’s Instituto Nacional de Ecología, preventing reintroduction requires constant vigilance. Through the 1980s, the numbers of Black Storm-Petrels seen near Los Coronados Islands decreased (Everett and Anderson 1991), but the numbers off southern California in general spike upward when the ocean warms during El Niño, as in 1992 (Ainley et al. 1995).
Least Storm-Petrel Oceanodroma microsoma
The Least Storm-Petrel nests on islands around Baja California and disperses north irregularly in late summer and fall across the international border. In some years it is seen on the ocean off San Diego County in flocks of hundreds, in others it is rare or absent.
Migration: Dates for the Least Storm-Petrel more or less near San Diego County range from 19 July (1927, one collected “a short distance north of the Mexican boundary,” Willett 1933) to 1 November (1977 one 9 miles off San Diego, D. W. Povey) and 10 November 1990 (1990, 41 at the Tanner Bank about 100 miles off San Diego, J. L. Dunn, AB 45:150, 1991). Two unseasonal records fall outside this interval: 35 off San Diego 2 June 1984 (G. McCaskie, AB 38:1061, 1984) and three seen from shore at La Jolla 19 April 1995 (S. Walens, NASFN 49:308, 1995). Exceptionally high estimates off San Diego are of 3000 on 17 September 1970 (AB 25:107, 1971), 3200 on 8 September 1979 (AB 34:200, 1980), and 3500 on 13 September 1992 (J. L. Dunn, AB 47:148, 1993).
The Least Storm-Petrel has been found once inside San Diego Bay, a bird picked up at Fisherman’s Landing (S8) 11 August 1996 (SDNHM 50231). Possibly it had come aboard a boat offshore, got trapped, then was tossed overboard when the crew was cleaning the boat.