Brandt’s Cormorant Phalacrocorax penicillatus
Brandt’s Cormorant is a strictly maritime bird, common on the ocean and San Diego Bay but not entering Mission Bay or the coastal lagoons. It can be seen far offshore—having colonies on all the Channel Islands and Los Coronados Islands—but is much more numerous within sight of land. The birds must come to coastal rocks or bluffs daily to roost and dry their plumage. Brandt’s Cormorant occurs in San Diego County most abundantly as a winter visitor, but some remain year round, and a few nest on cliff ledges at La Jolla.
Breeding distribution: Brandt’s Cormorants have nested at least sporadically at La Jolla (P7), on cliffs at La Jolla Caves, since before 1933, when Michael (1935a) called the colony “long established.” A thorough survey of the colony requires that it be inspected from the water or from the air; not all nests are visible to an observer standing on the ground at the best vantage points near La Jolla Cove. In an aerial survey on 19 May 1997, McChesney et al. (1998) photographed nine active nests. In 1999 and 2000, viewing the colony from shore, L. and M. Polinsky counted at least six active nests each year. In 2001, they counted at least five active nests on 28 April; on 9 July, a survey of the caves by kayak revealed 20 nests, though only two of these were still active. In 2002 there were at least two nests active by 24 February (K. L. Weaver); in 2003, there were three nests with chicks on 29 June (M. Sadowski). Many more birds remain around the colony than actually nest; counts at La Jolla in late spring and summer range up to 100 on 7 May 2000 (L. Polinsky).
Most Brandt’s Cormorants nest on offshore islands, with some on Los Coronados Islands just south of the border (Jehl 1977). The small colony at La Jolla is the only one on the mainland of southern California south of Santa Barbara County (McChesney et al. 1998). See Williams (1942) for two photographs of the colony taken in 1938.
In 1993, 1994, and 1995, a pair attempted to nest on the degaussing pier in the navy’s submarine base on the east side of Point Loma (S7). In 1993, the eggs hatched, but the nesting was interrupted when a minesweeper was degaussed and the disturbance kept the adults from coming to feed their chicks. The chicks were then taken into captivity and raised successfully, learning to dive and fish in a swimming pool and released back at the submarine base after fledging (M. F. Platter-Rieger, M. A. Faulkner). No chicks hatched from the attempts in 1994 and 1995.
From about 1985 to 1990 M. F. Platter-Rieger noted up to 25 Brandt’s Cormorants on nests on the west side of Point Loma, just north of the sewage-treatment plant. Since the early 1990s, however, she has seen no activity at this location, and McChesney et al. (1998) noted only roosting birds there in 1997. Both visibility and access at this site controlled by the navy are difficult, so the cormorant’s use of it is unclear.
Nonbreeding birds are seen through the summer along the San Diego County coast from La Jolla south (10 at Point Loma, S7, 17 June 1997, V. P. Johnson; up to 47 in north San Diego Bay 6 June 1995, K. L. Preston).
Nesting: At La Jolla, Brandt’s Cormorants nest on ledges on cliffs or in caves. They have been seen carrying both sticks and kelp as nest material. Nesting on man-made structures, as at Point Loma, is rare in this species (McChesney et al. 1998).
Brandt’s Cormorant nesting at La Jolla is notably unsynchronized. Michael (1935a) reported some birds beginning nest building on 21 December, others as late as 12 April. From 1997 to 2001 our dates for occupied nests ranged from 24 February (2002) to 9 July (2001). In 1980, three young fledged from two nests on 10 September (W. T. Everett), suggesting egg laying as late as early June.
Migration: Brandt’s Cormorant shifts north then south of its nesting colonies after the breeding season. In southern California it is much more numerous in winter than in summer (Briggs et al. 1987). In north San Diego Bay surveys from 1993 to 1995 (Mock et al. 1994, unpubl. data) found that numbers peaked in February and reached their nadir in July. In central San Diego Bay surveys from 1993 to 1994 found Brandt’s Cormorant from December to March only (Manning 1995). Even at Torrey Pines State Reserve, less than 5 miles from the colony at La Jolla, the species is recorded in spring no later than 4 May.
Winter: At this season Brandt’s Cormorant occurs all along the coast of San Diego County. In the county’s northern half, where there are fewer roost sites, it is less common. The maximum on any Oceanside Christmas bird count is 71 on 29 December 1996, but an exceptional 700 were off Agua Hedionda Lagoon (I6) 10 January 1999 (P. A. Ginsburg). In southern San Diego County numbers are highest at Torrey Pines State Reserve (N7/O7; 520 on 2 January 1998, S. E. Smith), La Jolla (300 on 28 January 2000, L. Polinsky), Point Loma (200 on 27 February 2001, V. P. Johnson), and on north San Diego Bay (S8; 343 on 22 February 1993, Mock et al. 1994; 400 on 10 February 2002, K. L. Weaver). Although Brandt’s Cormorant is second only to Heermann’s Gull as the most abundant bird on north San Diego Bay and variably common on central San Diego Bay (up to 174 on 16 February 1993, Mock et al. 1994), it is rare to absent from south San Diego Bay south of National City (Macdonald et al. 1990, Manning 1995). Flocks can be seen commuting between Los Coronados Islands and Point Loma.
Conservation: Brandt’s Cormorants suffer from contamination with pesticides washed into the ocean, from oil spills, and from human disturbance of nesting colonies (Wallace and Wallace 1998). Michael (1935a) mentioned boys flushing cormorants from their nests at La Jolla by dropping objects on them from the tops of the cliffs. The greatest variations in the birds’ numbers and nesting success result from the effect of El Niño on the abundance of fish. When El Niño arrives, the ocean warms, and the food supply is depressed, Brandt’s Cormorants raise fewer young or forgo nesting entirely (Boekelheide et al. 1990).
The colony at La Jolla has not been studied consistently enough for its variations to be understood. It was active at least in 1933–34 (Michael 1935a), 1938 (Williams 1942), and 1980 (W. T. Everett) but vacant in June 1991 (McChesney et al. 1998). On 4 May 1995, K. B. Clark noted one active nest and another bird carrying nest material. Surveys for this atlas give the most continuous record of the colony to date and show it has been occupied annually at least since 1997. In 1997, McChesney et al. (1998) noted an increase in Brandt’s Cormorants nesting throughout southern California (primarily on the Channel Islands) from previous surveys; a dearth of suitable nest sites may be the factor constraining the breeding population.
Taxonomy: No subspecies. On the basis of skeletal differences, Siegel-Causey (1988) recommended that the genus Phalacrocorax, currently encompassing all cormorants, be broken up, Brandt’s going into Compsohaliaeus.
Double-crested Cormorant Phalacrocorax auritus
The Double-crested is our most versatile cormorant, occurring commonly as a nonbreeding visitor on water both fresh and salt. It nests near San Diego County on the Channel and Los Coronados islands and at the Salton Sea; two colonies within the county have formed only since 1988. The Double-crested Cormorant has had a difficult and contentious relationship with humanity, exploiting reservoirs and aquaculture but suffering from disturbance, pesticide contamination, and direct control as a pest. At the beginning of the 21st century, the cormorants were winning, increasing in numbers and establishing new colonies.
Breeding distribution: Double-crested Cormorants nested in two colonies during the atlas period, in the salt works at the south end of San Diego Bay (U10) and at the upper end of Sweetwater Reservoir (S13). The colony in the salt works formed in 1988, when the birds began nesting on a mobile dredge. Since 1997, maximum numbers of nests have been 51 on 1 June 1997 (M. R. Smith) and 71 on 30 June 1999 (R. T. Patton). The dredge has remained the focus of the colony, but in some years, such as 1993 (Stadtlander 1993), 1994 (Terp and Pavelka 1999), 1999, and 2001 (R. T. Patton), some birds nest on the ground on the dikes of the salt works. Nineteen pairs nested on the ground in 1993 (Stadtlander 1993). One such nest on 18 July 2001 accounts for the cormorant appearing as a nesting bird in atlas square V10 as well as U10—the salt works straddle both squares.
At Sweetwater Reservoir, the colony first formed in 1996, the birds building in a single tree. By 8 May 1998 they had spread to nine trees with a total of 28 nests in which adults were incubating or brooding. On 24 May 2001, the colony numbered 17 occupied nests in two trees (P. Famolaro).
Nonbreeding birds are locally common at other localities through the summer: 18 at Lake Henshaw (G17) 18 June 2000 (P. Unitt), 30 at San Elijo Lagoon (L7) 12 July 1998 (B. C. Moore), 18 at San Vicente Reservoir (N13) 20 May 2001 (R. and S. L. Breisch), 34 in north San Diego Bay (S8) 26 May 2000 (R. T. Patton), 26 at Barrett Lake (S19) 4 June 2000 (R. and S. L. Breisch), and 20 at Lower Otay Lake (U13) 8 May 1999 (P. Unitt). Summering Double-crested Cormorants are widely scattered on inland lakes, as high as Cuyamaca Lake (M20; one on 25 June 1998, A. P. and T. E. Keenan) and as far east as Tule Lake (T27; up to two on 6 June 2001, J. K. Wilson).
Nesting: The Double-crested Cormorant builds a bulky nest of sticks and debris, placing it usually in a tree surrounded by water or on the ground in a site isolated from predators. On the dredge in the salt works, some nests are well supported on sheets of metal but others are balanced precariously across two cables; some of the latter blew down in 2001. Some Double-crested Cormorant nests, however, persist for years, the pair refurbishing them annually.
Because Double-crested Cormorant nests are typically difficult to inspect closely—and vulnerable to disturbance—there are few data on their nesting schedule in San Diego County. Reports of nestlings are concentrated from late June to late July, suggesting that egg laying ranges from about mid April to mid June. In the early 20th century eggs were collected at Lake Henshaw (G17) on 15 and 30 May. Reports of occupied nests, however, range from 31 March to 11 August. In 1998, nesting at the salt works began by 3 April and continued through late July (Terp and Pavelka 1999).
Migration: The Double-crested Cormorant is far more abundant in San Diego County in fall and winter than in spring and summer. Surveys of San Diego Bay (Mock et al. 1994, Stadtlander and Konecny 1994, Manning 1995) and San Elijo Lagoon (King et al. 1987) found cormorant numbers peaking variously from September to February and reaching their lows in June and July. In the salt works Stadtlander and Konecny (1994) recorded their maximum of 1012 on 17 November 1993.
In the Anza–Borrego Desert, the approximately 15 records range from 29 October (1991; two at the Roadrunner Club, F24, A. G. Morley) to 9 May (2001; one at Borrego Springs, G24, P. D. Ache). All are from artificial ponds in the Borrego Valley except for a sighting of two flying over Hawk Canyon (H27) 10 April 1988 (P. D. Jorgensen).
An unusual record of migrants on the coastal slope was of 44 in flight near Dulzura (T16) 21 April 2001 (S. Yamagata, T. Stands).
Winter: The Double-crested Cormorant is not only more numerous in the winter but more widespread. From 1997 to 2002 it was recorded in 47 atlas squares in winter but not the breeding season versus 16 for the converse. It occurs all along the coast, with up to 626 at Point Loma (S7) 16 December 2000 (M. W. Klein), 300 in Mission Bay (Q8) 18 December 1998 (J. C. Worley), and 300 at the San Diego River flood-control channel (R8) 28 February 1999 (B. C. Moore). It is no less common on inland lakes, with up to 218 on Lake San Marcos (J8) 27 December 1997 (J. O. Zimmer), 250 on Lake Hodges (K10) 6 December 1999 (R. L. Barber), and 300 at the Wild Animal Park (J12) 8 January 2000 (D. and D. Bylin). Wintering Double-crested Cormorants occur as high as 3900 feet at Corte Madera Lake (Q20; up to seven on 20 February 1999, G. L. Rogers) and 4600 feet at Cuyamaca Lake (up to 33 on 14 December 1999, A. P. and T. E. Keenan). In Borrego Springs (G24) we had only two records of single individuals during the atlas period (P. D. Ache), but an exceptional 59 were at the Roadrunner Club 10 January 1993 (A. G. Morley).
Conservation: The Double-crested Cormorant’s numbers decreased because of persecution early in the 20th century, then because of pesticide contamination in the 1950s and 1960s, which led to nesting failure (Gress et al. 1973). In the last quarter of the century, however, the population over much of North America increased rapidly (Hatch and Weseloh 1999). The increase included California, aided by adaptation to artificial nest sites (Carter et al. 1995). In San Diego County the Double-crested Cormorant has benefited from the building of reservoirs and the reservoirs’ being stocked with fish. Results of the Oceanside and Rancho Santa Fe Christmas bird counts show no great change, but the San Diego count averaged 296 Double-crested Cormorants per year from 1965 to 1974, 735 from 1997 to 2001. During its first ten years, 1986–94, the Escondido count averaged 100, but during the atlas period the figure rose to 263.
The cormorant’s career of decline and recovery is also reflected in its status as a breeding bird in San Diego County. Shortly after Lake Henshaw was created, cormorants colonized, nesting “plentifully” at least in 1928 and 1932 (J. B. Dixon in Willett 1933; two egg sets collected in each year, WFVZ). The colony was evidently soon eliminated, however; fishermen often see cormorants as competitors. For many years the Double-crested Cormorant occurred in San Diego County as a nonbreeding visitor only. The colony at the salt works began with one or two pairs in 1988 (E. Copper), increasing to 14 nests the following year (Macdonald et al. 1990). The addition of the Sweetwater Reservoir colony in 1996 will probably not be the last.
Taxonomy: Phalacrocorax a. albociliatus Ridgway, 1884, with the crests of breeding adults partly white, is the subspecies of the Double-crested Cormorant in and near California.
Pelagic Cormorant Phalacrocorax pelagicus
The Pelagic is the least numerous and least widespread of San Diego County’s three cormorants, easily overlooked among the Brandt’s Cormorants that are always more abundant in its habitat. The Pelagic Cormorant has a close association with rocky shorelines, as it roosts on exposed rocks and forages primarily over submerged rocks. In San Diego County it is primarily a winter visitor, though occasional birds occur in summer and suggest the possibility of nesting at La Jolla or Point Loma.
Winter: In San Diego County, the Pelagic Cormorant occurs primarily along the coast from Torrey Pines State Reserve (N7) south to Point Loma (S7). It is generally uncommon; from 1997 to 2002 our only counts of more than eight individuals were of 10 at La Jolla 4 January 1998 (B. C. Moore) and 36 at the same location 2 December 1998 (L. and M. Polinsky). On the San Diego Christmas bird count, where the species is normally found only at Point Loma, totals during the atlas period ranged only from five to nine, but occasional years see larger influxes, yielding counts as high as 120 on 18 December 1982 and 127 on 19 December 1987.
No Pelagic Cormorants were reported from northern San Diego County during the atlas period, but a few occur occasionally at the entrance to the Oceanside harbor (H5). The species was noted on 10 of 27 Oceanside Christmas bird counts 1976–2001 with a maximum of five on 24 December 1994. Inside San Diego Bay the Pelagic Cormorant is uncommon in the north bay, north of the bridge. Mock et al. (1994) called it fairly common to common there, but in weekly surveys through 1993 their only count of more than seven was of 12 on 7 December. Similar surveys of central San Diego Bay in 1994 yielded only one Pelagic Cormorant (Preston and Mock 1995). There are no records from the south bay or Mission Bay.
Migration: The Pelagic Cormorant occurs in San Diego County principally from October through March. From 1997 to 2001 our only record later than 1 April was of one at Torrey Pines State Reserve (N7) 3 June 2001 (P. A. Ginsburg). During their surveys of north San Diego Bay in 1993, Mock et al. (1994) recorded the species in every month of the year except November, but only a single individual in June and July.
Breeding distribution: The Pelagic Cormorant is not confirmed to nest in San Diego County, but nesting is possible. From about 1985 to 1990 M. F. Platter-Rieger noted some Pelagic Cormorants with apparently nesting Brandt’s Cormorants on the steep slopes of Point Loma north of the sewage-treatment plant. On 29 June 2003, M. Sadowski noted five to nine coming and going from the cliffs at La Jolla Caves. On 6 July, he surveyed the cliffs from a kayak and counted six Pelagic Cormorants, but they were not associated with any nests.
San Diego County lies near the southern tip of the Pelagic Cormorant’s breeding range. Los Coronados Islands were the southernmost known breeding locality until 2000, when Palacios and Mellink (2000) reported two pairs nesting on Isla Todos Santos off Ensenada.
Conservation: No trend in Pelagic Cormorant numbers in or near San Diego County is clear, but at the Farallon Islands off San Francisco the population varies greatly and fails to breed when El Niño suppresses the supply of fish (Ainley et al. 1994). Increases in ocean temperature that reduce the food supply and have already affected some other birds could result in the Pelagic Cormorant’s range retracting north, out of San Diego County.
Taxonomy: Pelagic Cormorants south of southern British Columbia have long been recognized as the subspecies P. p. resplendens Audubon, 1838, smaller than the nominate subspecies occurring farther north. The measurements tabulated by Hobson (1997), however, show great overlap, too much for the subspecies to be recognized on the basis of any single measurement.