Plovers — Family Charadriidae
Black-bellied Plover Pluvialis squatarola
The Black-bellied Plover is one of San Diego County’s more numerous wintering shorebirds with about 1500 to 3000 annually. The species prefers tidal mudflats but uses a variety of habitats including brackish lagoons, sandy beaches, and rocky shorelines. Away from the coast the Black-bellied Plover is now rare, as the agricultural fields it formerly frequented inland are almost gone.
Winter: Because of its using sandy beaches, the Black-bellied Plover is found all along San Diego County’s coast. Its numbers are by far the greatest, however, on the mudflats around south San Diego Bay. On their weekly counts in and near the salt works (U10/V10), 1993–94, Stadtlander and Konecny (1994) found an average of about 500–600 in December and January and a maximum of 1155 on 1 December 1993. In the same area, the San Diego Christmas bird count 15 December 2001 yielded 1418 (D. C. Seals et al.). Numbers can be large elsewhere on San Diego Bay (312 at the D St. fill, T10, 18 February 2000, R. T. Patton), in northeastern Mission Bay (Q8; up to 526 on 18 December 1998, J. C. Worley), and in the Tijuana River estuary (V10; 150 on 19 December 1998, A. DeBolt). Because the Black-bellied Plover forages individually rather than in flocks, such large numbers are seen generally when the birds congregate on dry ground to loaf and wait out the high tide.
In northern San Diego County wintering Black-bellied Plovers are less common. The Oceanside Christmas bird count averages 100, the Rancho Santa Fe count 43. Counts of 85 at San Onofre State Beach (C1) 28 January 2001 (R. Breisch), 200 at the Santa Margarita River mouth (G4) 25 January 1998 (B. C. Moore), and 80 in the east basin of Batiquitos Lagoon (J7) 26 December 1998 (R. and A. Campbell) were exceptionally high for this area. Away from coastal wetlands the Black-bellied Plover is generally uncommon. A high count for a bluff-backed beach is 37 at San Elijo State Beach (L7) 8 February 2004 (E. Garnica), for rocky shoreline, 27 at Point Loma 16 December 2000 (M. W. Klein).
From 1997 to 2002 we found wintering Black-bellied Plovers inland only at the east end of Lake Hodges (K11; two on 13 December 1999, B. C. Moore; one still present 26 December, E. C. Hall) and along the San Dieguito River in San Dieguito Valley (M8; up to 40 on 10 January 1998, R. T. Patton) and Osuna Valley (L8; up to 15 on 27 December 1998, A. Mauro). One at Lake Henshaw (G17) 16 December 2002 (P. Unitt) is the only one recorded on a Lake Henshaw Christmas bird count.
Migration: As for all shorebirds, understanding Black-bellied Plover migration requires that the plumage types be recorded separately, as nonbreeding birds summer commonly around south San Diego Bay (55 on 24 June 1988, Macdonald et al. 1990) and in the Tijuana River estuary (30 on 6 June 1998, B. C. Moore). Two hundred around south San Diego Bay 1 June 1987 (R. E. Webster, AB 41:1487, 1987) were an unusually large number for summering birds. A few summer elsewhere along the coast (up to eight at Batiquitos Lagoon 4 June 1999, B. C. Moore). Migrants begin returning in July and finish leaving in May. There is no clear peak of migration in spring but there is in fall, with the arrival of juveniles in August and September.
Well inland, migrating Black-bellied Plovers are rare. Besides a few scattered individuals at lakes Hodges and Henshaw, 184 fall migrants were at Lake Henshaw 31 July 1981 and 30 spring migrants flew over Palomar Mountain (D15) 16 April 1982 (R. Higson, AB 36: 894, 1982).
Conservation: Development of Mission and San Diego bays eliminated a large fraction of the tidal mudflats where Black-bellied Plovers feed, but there are no adequate data suggesting any change in the species’ status along the coast. Inland, however, urban development supplanting agriculture has eliminated most of the fields the plovers formerly used; far fewer occur inland now than in the 1960s and 1970s.
Taxonomy: The subspecies maintained by Engelmoer and Roselaar (1998) are differentiated insufficiently for taxonomic recognition (Patten et al. 2003).
American Golden Plover Pluvialis dominica
The American Golden Plover occurs—or occurred—in San Diego County as a rare fall migrant. Its primary site was the Tijuana River valley, where the extensive irrigated pastures that once attracted the birds no longer exist.
Migration: The American Golden Plover has been seen in San Diego County mainly from mid September to late October. The maximum number recorded was 15 in the Tijuana River valley 8 October 1966 (G. McCaskie). These could have included Pacific Golden Plovers as well; at that time criteria for distinguishing the golden plovers in the field were not well understood. The only specimen of the American was collected there 18 October 1972 (SDNHM 38234). Extreme dates are 26 July (1980, AB 34:930, 1980) and 23 November (1992, E. R. Lichtwardt, AB 47:149, 1992). With a couple of sod farms being the only agricultural fields remaining in the Tijuana River valley, the American Golden Plover has become less than annual. One was there 30 September–23 October 2003 (G. McCaskie). Of the spring records of golden plovers in San Diego County, none is certainly of the American.
Pacific Golden Plover Pluvialis fulva
Many migrating Pacific Golden Plovers cross the North Pacific Ocean, but only a few follow the west coast of North America. Only since the 1990s have criteria for distinguishing them in the field from the American Golden Plover become widely known, and specimens in California are few (none from San Diego County). Thus the status of the Pacific Golden Plover could use further clarification, but apparently one to three reach the county’s coastal wetlands each year, in both migration and winter. Of this pair of species, only the Pacific has been confirmed wintering on North America’s Pacific coast.
Winter: In San Diego County, the Pacific Golden Plover has been found wintering in the San Dieguito River estuary (M7; 3 January–9 February 2002, N. Ferguson, NAB 56:223, 2002), Mission Bay (Q8; 10 December 2000, E. Wallace), at the San Diego River mouth (R7; one or two annually 1962–74, G. McCaskie), San Diego Bay at Coronado (S9; 12 January 1908, Torrey 1909), in the Tijuana River valley (up to six in the 1960s, AFN 21:458, 1967; 23:521, 1969), and, most frequently, in the Tijuana estuary (V10). From 1999 to 2002, one individual apparently returned to that site annually, and up to three were there 30–31 January 1999 (J. L. Coatsworth, NAB 53:208, 1999).
Migration: Because of the difficulty in distinguishing the Pacific Golden Plover from the American, especially when the birds are in molt between their breeding and winter plumages, the migration schedules of both species are uncertain. The Pacific has been reported at least from 1 August (1995, San Elijo Lagoon, P. A. Ginsburg, NASFN 50:114, 1996) to 11 May (1997, south San Diego Bay, D. Parker, FN 51:927, 1997; 2000, Tijuana River mouth, R. T. Patton, NAB 54:221, 327, 2000). A golden plover in the Tijuana estuary 27 June 1998 (C. G. Edwards) was most likely the Pacific wintering there, returned early. The identification of one at the San Diego River mouth 4–8 June 1983 is uncertain (D. B. King, AB 37:912, 1983). A spring migrant at Point Loma 10 May 1985 was at an atypical site (R. E. Webster, AB 39:350, 1985).
Taxonomy: The Pacific and American Golden Plovers were considered subspecies until Connors et al. (1993) confirmed assortative breeding where both occur in western Alaska.
Snowy Plover Charadrius alexandrinus
Nesting on beaches, dunes, and salt flats, the Snowy Plover is among San Diego County’s scarcest and most threatened breeding birds. In 1993 the U.S. Fish and Wildlife Service listed it as threatened along the entire Pacific coast. Thorough surveys 1995–98 put the county’s breeding population between 240 and 325 individuals, most concentrated in two areas, Camp Pendleton and the Silver Strand (Powell et al. 2002). Surveys from 1978 to 1998 suggest the decline of this once common bird has continued. When not breeding the Snowy Plover is more widespread along the county’s coast but it is not much more numerous, in spite of considerable migration. Human disturbance of the remaining habitat and a high level of predation mean that intensive management is needed to sustain the population.
Breeding distribution: Powell et al. (2002) surveyed San Diego County’s coastline intensively from 1994 to 1998 and provided an exhaustive view of the Snowy Plover’s distribution. Their detailed table enumerated nests rather than birds per site; because of multiple clutches per year, this figure is greater than the number of nesting pairs by 35%. Tracking of banded birds showed that, within a single breeding season, some individuals shift from site to site, although most remain at one site.
These variables considered, about half the population breeds in Camp Pendleton, with six to eight nests per year at the mouths of Aliso and French creeks (F4) and 67 to 88 at the Santa Margarita River mouth (G4). The high count of individual plovers was 120 at the latter site 11 June 1997 (B. L. Peterson). At Batiquitos Lagoon (J6/J7), the plovers nest at both the east and west ends on sandy fills installed to provide nesting habitat for the Least Tern, as part of a lagoon-enhancement project. The number of nests at Batiquitos Lagoon 1995–98 varied from 15 to 40. At San Elijo Lagoon (L7), as a result of variable water levels, the plover nests only intermittently, with five nests in 1994, none for the next four years, and one in 1999 (R. T. Patton). Mariner’s Point in Mission Bay (R7) hosted one unsuccessful pair in 1995 and none since.
The Silver Strand (T9) is the plover’s other main breeding site in San Diego County, with 17 to 38 nests in the Naval Amphibious Base (both bay and ocean shores) and 4 to 10 at Silver Strand State Beach. Zero to two nests per year were found at the Naval Radio Station at the south end of the strand (U10/V10). Four Snowy Plovers at North Island (S8) 26 May 2000 included a fledgling (R. T. Patton). Within San Diego Bay, Powell et al. (2002) found 2 to 13 nests per year at the D Street fill in the Sweetwater River estuary (T10) and zero to four at the salt works (U10/V10). One pair nested at the D Street fill in 1999, another at the Chula Vista Wildlife Reserve in 1998 (R. T. Patton). Around the Tijuana River mouth (V10/W10) the plovers nest on both the north and south sides, with 11 to 17 nests 1995–98 (Powell et al. 2002) and 12 in 2001 (R. T. Patton).
In 2002 and 2003 the county’s population was slightly less than the 240–325 found 1995–98, with 102 estimated pairs (323 nests) in 2002 and 233 individuals (but only 67 nests) in 2003 (R. T. Patton).
Nesting: The Snowy Plover nests in a shallow scrape in sand or dried mud, variably lined with pebbles, bits of shell, or bits of vegetation. Powell et al. (2002) charted the species’ breeding season on the basis of 801 nests. Their earliest nest was 10 March; egg laying peaked in late May and ended in late July. Hatching begins in the latter half of April, peaks in the latter half of June, and ends in the latter half of August. Even successful females may lay up to three clutches in a breeding season, helped along by their habit of leaving the chicks with the male while they start a new nest with another male (Page et al. 1995).
Migration: The Snowy Plover is highly mobile: even during the breeding season banded birds have moved as far as 500 miles along the California coast between successive broods (Stenzel et al. 1994). A few birds are seen at places where they do not nest even near the peak of egg laying (up to four at Los Peñasquitos Lagoon, N7, 27 April 1999, M. B. Stowe). Migrants away from nesting sites become more numerous by August (15 at San Onofre State Beach, C1, 6 August 1999, P. A. Ginsburg). Snowy Plovers banded as far north as Santa Cruz County have been seen wintering in San Diego; birds banded in San Diego County have been seen north to San Luis Obispo County, west to San Clemente Island, and south to Scammon’s Lagoon in Baja California (Powell et al. 2002). Each year, however, 15–27% of plovers banded by Powell et al. wintered near their nesting sites.
Inland in San Diego County, the Snowy Plover is rare, recorded only at lakes Henshaw (G17; one on 5 November 1978, AB 33:213, 1979) and Hodges (K10/K11; noted once in spring, 11 May 1985, and sporadically in fall from 7 July [2 in 1982] to 2 October [1 in 1982] K. L. Weaver). Exchange of birds between the coast and inland sites is regular, however (Page et al. 1995).
Winter: Snowy Plovers winter widely along San Diego County’s coast, using not only their nesting sites but also several beaches and estuaries where they do not nest. During the atlas period our winter counts ranged up to 90 at the Tijuana River mouth 15 December 2001 (R. B. Riggan), 70 along the Silver Strand 19 December 1998 (N. Osborn), 90 at North Island 11 January 2002 (R. T. Patton), 52 in northeastern Mission Bay (Q8) 7 December 1998 (J. C. Worley), and 34 at San Onofre State Beach 28 January 2001 (J. M. and B. Hargrove). Powell et al. (2002) reported up to 177 at the Sweetwater River mouth but on occasion found zero birds at almost every site—flocks sometimes forage on one beach, then rest on another (B. L. Peterson). Powell et al. estimated the county’s winter population at 227–367 individuals. A cooperative census the length of San Diego County’s coast 10–13 January 2001 yielded 390; another 8–11 January 2003 yielded 547. The most significant increases were in the north county, where projects to replenish beach sand have augmented the plover’s habitat (R. T. Patton).
The single winter record inland is of one at Lake Henshaw 21 December 1998 (S. J. Montgomery).
Conservation: Stephens (1919a) called the Snowy Plover “abundant” in San Diego County. In 1978, Page and Stenzel (1981) censused 257 individuals in the county; in 1989, Page et al. (1991), repeating the survey, censused only 149. The higher numbers found by Powell et al. (2002) are not comparable with the results of the earlier surveys because the more recent study was much more intensive and covered areas missed by the earlier ones. The plovers have abandoned Agua Hedionda Lagoon (I6), site of 27 pairs in 1978, and become sporadic at San Elijo Lagoon, site of 12 pairs in 1978. The birds have concentrated at the Santa Margarita River mouth and the Naval Amphibious Base, perhaps because predators are controlled at these places, under a program designed to protect nesting Least Terns. Although the endangered birds nesting on these military lands are monitored and managed intensively, changes in military policy toward endangered species—already announced—could change the plover’s status quickly. The effort to restore Batiquitos Lagoon, by establishing tidal flow and providing nesting habitat, attracted plovers (Powell et al. 2002), though their nesting success there was low (Powell and Collier 2000).
At many sites, however, disturbance and nest predation are constant problems. The plover’s productivity in San Diego County is less than in coastal northern California (Powell et al. 2002). The trend has been for the species to disappear from sites accessible to the public, like Agua Hedionda Lagoon and the Tijuana River estuary. Development surrounding almost all sites concentrates predators there, leading to further conflicts. The plover’s only defenses are camouflage and renesting after losing a clutch. All ground-nesting birds retreat from urbanization, and in San Diego County none has retreated more than the Snowy Plover.
Taxonomy: The subspecies of the Snowy Plover in North America is C. a. nivosus (Cassin, 1858).
Wilson’s Plover Charadrius wilsonia
Wilson’s Plover is locally common in Baja California Sur but only a rare vagrant along the Pacific coast north of the international border. Of nine well-supported records from California, four are from San Diego County, in April, May, and June. All these Wilson’s Plovers were on sandy beaches.
Migration: Ingersoll (1895) found California’s Wilson’s Plover at Pacific Beach (Q7) 24 June 1894, collecting it 29 June (MVZ 31920). One at the Tijuana River mouth (V10) 9 April 1991 (D. Parker-Chapman) and one at Delta Beach, Silver Strand (T9), 27 April–1 May 1998 (E. Copper) were both photographed (Heindel and Garrett 1995, Erickson and Hamilton 2001). The California Bird Records Committee also accepted a sight record from North Island Naval Air Station (S8) 5 May 2000 (R. T. Patton, McKee and Erickson 2002). A few other published sightings lack details, though the one by Ingersoll (1918) at Imperial Beach (V10) 11 May 1918 was likely valid.
Intensive monitoring of Least Terns and Snowy Plovers along San Diego County’s beaches accounts for the apparently increased frequency Wilson’s Plover here.
Taxonomy: California’s specimen of Wilson’s Plover is C. w. beldingi (Ridgway, 1919), resident along the Pacific coast from Baja California south to Peru.
Semipalmated Plover Charadrius semipalmatus
The Semipalmated Plover prefers coastal mudflats, as might be predicted from its mud-colored upperparts. Small numbers also visit sandy beaches and inland lakeshores. Like other shorebirds that breed in the far north, it spends most of its life in its winter range: the last northbound migrants and the first southbound migrants almost meet each other in June. Small numbers of nonbreeders remain year round. The Semipalmated is especially common in fall migration but common in winter as well—the number wintering in San Diego County is about 750 to 1000.
Winter: Wintering Semipalmated Plovers are well distributed along San Diego County’s coast, as a result of the birds’ using beaches as well as mudflats. In spite of the lack of extensive mudflats in this heavily developed part of Mission Bay, El Carmel Point (Q7) emerged as a hot spot for the species, with up to 250 on 12 February 2000 (L. Polinsky) and 400–500 on 24 October 1998 (J. L. Coatsworth). Elsewhere wintering Semipalmated Plovers are often common at north county lagoons (up to 77 at San Elijo Lagoon, L7, 23 December 2001, E. Garnica; 75 at Agua Hedionda Lagoon, I6, 12 February 2000, J. Ciarletta), in the San Diego River flood-control channel (R8; 30 on 5 January 1998, M. B. Stowe), around San Diego Bay (maximum 321 in the salt works, U10/V10, 26 January 1994, Stadtlander and Konecny 1994), and in the Tijuana River estuary (V10; 75 on 15 December 2001, R. B. Riggan). Our maximum numbers on sandy beaches were 23 at Encinitas (K6) 10 December 2000 (E. Garnica) and 21 at Torrey Pines (O7) 11 February 2000 (D. G. Seay).
Inland the Semipalmated Plover is uncommon in migration and generally rare in winter, when it has been found only in the coastal lowland. From 1997 to 2002 our sites for the species inland in winter were O’Neill Lake (E6; up to five on 14 December 1997, B. C. Moore), Lake Hodges (K10/K11; up to 30 on 22 December 2000, R. L. Barber), and Sweetwater Reservoir (S12/S13; up to two on 20 December 1997 and 18 December 1999, P. Famolaro).
Migration: Adult Semipalmated Plovers begin returning in late June or early July; from 1997 to 2001 our earliest was one at the Santa Margarita River mouth (G4) 3 July 1999 (P. A. Ginsburg). Fall migration peaks in September and October with the arrival of juveniles. There is no clear peak of spring migrants, but the species occurs rarely at inland sites where it does not winter in both spring and fall migration (Unitt 1984). Our only record for southeastern San Diego County was of one at the upper end of Lake Morena (S22) 13 August 2000 (R. and S. L. Breisch). In the Anza–Borrego Desert all records are for spring: one at Middle Willows (C22) 3 May 1975 (G. Salzberger), two there 29 April 1997 (P. D. Jorgensen), six at Borrego Springs (G24) 25 April 1998, two there 15 April 2000 (P. D. Ache), and one at the Borrego sewage ponds (H25) 29 April 1990 (A. G. Morley).
Though a few migrants may still be moving north in early June, most Semipalmated Plovers seen then are probably staying for the summer. Maximum numbers are 16 at Batiquitos Lagoon (J7) 7 June 1998 (C. C. Gorman), 45 around south San Diego Bay 1 June 1987 (R. E. Webster, AB 41:1487, 1987), at least 40 there 12 June 1989 (Macdonald et al. 1990), and 20 in the Tijuana River estuary 6 June 1998 (B. C. Moore)
Conservation: Although the mudflats around San Diego Bay are much reduced from their primitive extent, results of San Diego Christmas bird counts 1953–2002 suggest a possible modest trend toward increase over the latter half of the 20th century. From 1953 to 1977 the count averaged 0.22 Semipalmated Plovers per party-hour, whereas from 1978 to 2002 it averaged 0.39.
Killdeer Charadrius vociferus
Being adapted to use disturbed bare ground and a minimum of water enabled the Killdeer to become San Diego County’s most widespread shorebird. It is common from coastal wetlands and bayfills to agricultural fields, lakeshores, golf courses, ball fields, sand mines, graded clearings, cobbly washes with intermittent pools, and even some oases in the Anza–Borrego Desert. Despite the Killdeer’s predilection for bare dry dirt, its distribution suggests it needs water to drink, at least during the breeding season. One of the few shorebirds that breeds in San Diego County, Killdeer appears more abundant in winter, perhaps just a result of the local population clumping into loose flocks.
Breeding distribution: In San Diego County the Killdeer is most widespread in the coastal lowland, at coastal wetlands (up to 31 at Los Peñasquitos Lagoon, N7, 2 April 2000, D. K. Adams) and in inland valleys (up to 89 along the San Diego River between Santee and Lakeside, P13, 23 April 1998, W. E. Haas). At higher elevations, more rugged topography and less imported water mean the species’ distribution is patchier, but it is just as common where habitat is available (38 on the north side of Lake Morena, S21, 7 July 2001, R. and S. L. Breisch; 50 at Tule Lake, T27, 27 June 2001, J. K. Wilson). If the habitat is suitable, the Killdeer is not constrained in San Diego County by elevation, as it breeds up to 5400 feet at Big Laguna Lake (O23; 10, including young, 9–10 June 2001, C. G. Edwards).
In the Anza–Borrego Desert, the Killdeer breeds widely in the irrigated parts of the Borrego Valley (up to 16 at golf-course ponds in Borrego Springs, G24, 25 April 1998, P. D. Ache). Along Coyote Creek the Killdeer breeds regularly at both Lower Willows (D23; up to four on 19 May 2001, M. L. Gabel) and Middle Willows (C22; up to seven, including young, on 6 May 2001, P. D. Jorgensen). Near the junction of San Felipe Creek and Grapevine Canyon (I23), where the species was absent from 1997 to 2001, it bred in 1982, with nests on 7 and 25 April (P. D. Jorgensen, ABDSP database). Clearing in 2002 of the tamarisk clogging Sentenac Ciénaga (J23) allowed a pair to colonize in 2003 (J. R. Barth); our only Killdeer in this area from 1997 to 2002 was a single individual at nearby Scissors Crossing (J22) 25 May 1998 (E. C. Hall). In the southern section of the desert the Killdeer’s only site is Carrizo Marsh (O29; up to four, including a pair in distraction display, on 25 April 2001, M. C. Jorgensen).
Nesting: The Killdeer nests in a scrape on the ground, lining it with shells, pebbles, or debris. It compensates for the nest’s being so exposed by distracting predators—and birders—with loud calls and conspicuous displays of feigned broken wings. It also nests regularly on flat gravel rooftops, obliging the chicks to leap to the ground. Our records of nests with eggs extend from 5 March (1998, Rancho Santa Fe, L8, A. Mauro) to 10 July (2001, two nests, D Street fill in Sweetwater River estuary, T10, R. T. Patton), an interval considerably wider than the 18 March–10 June known from egg sets collected 1901–64. A chick at Valhalla High School (R14) 22 March 2001 suggests egg laying as early as the last week of February (S. Brad).
Migration: There is little evidence in San Diego County for Killdeers migrating through areas where they neither nest nor winter. Possible migrants through the Anza–Borrego Desert are one in Culp Valley (G23/H23) 18 March 1992 (M. L. Gabel) and up to two near Tamarisk Grove (I24) 19–21 April 1985 (N. Foley).
Winter: The Killdeer’s distribution in San Diego County in winter differs little from that in the breeding season, but the birds are seen often in flocks rather than in pairs. Most are still in the coastal lowland, but our largest flock, of 150 on 25 January 1998, was at about 2400 feet elevation in Long Potrero (T20; D. C. Seals). In spite of the freezing temperatures, the Killdeer is fairly regular in winter at Big Laguna Lake (up to six on 23 February 2002, K. J. Winter). The species’ desert locations are the same as in the breeding season except for Tamarisk Grove, site of three on 2 December 1998 (P. K. Nelson).
Conservation: The Killdeer benefits from many human modifications of the San Diego County environment such as importation of water, maintenance of lawns, and bulldozing of brush. But a countryside dominated by agriculture and pastures is far more favorable to the Killdeer than one dominated by pavement, buildings, and manicured landscaping. Presumably as a result of more intensive urbanization, the number of Killdeers per party-hour on San Diego Christmas bird counts declined from 2.05 from 1953 to 1977 to 1.23 from 1978 to 2002.
Taxonomy: Killdeers throughout North America are nominate C. v. vociferus Linnaeus, 1758.
Mountain Plover Charadrius montanus
The Mountain Plover is one of North America’s most seriously threatened birds. The U.S. Fish and Wildlife Service proposed it be listed an endangered species in 1999, then canceled the proposal in 2003. The primary factor decimating the plover is apparently habitat change in its breeding range on the Great Plains and intermountain plateaus: conversion of short-grass prairie to cropland and pastures of taller grass and elimination of the prairie dogs that once kept the prairie partly open (Leachman and Osmundson 1990, Knopf 1996). But in its winter range in southern California the plover has also lost much of its habitat, open plains and plowed fields of bare dirt. The Mountain Plover’s former regular wintering in San Diego County came to an end in 1991. Only a single migrant has been reported since then.
Winter: Though Stephens (1919a) called the Mountain Plover “rather common” in San Diego County, specific locations recorded for the species are rather few: Stuart Mesa (G4; eight on 22 December 1979, E. Copper), San Luis Rey (G6; 6 March 1960, A. M. Rea), Warner Valley along Highway 79 near Highway S2 (G18; up to 50 on 18 and 29 December 1981, C. G. Edwards), Ocotillo Wells (I28/I29; three on 18 March 1978, AB 32:1055, 1978), Lake Cuyamaca (L21; one on 9 November 1980, D. Parker), the airfield in what is currently known as Marine Corps Air Station Miramar (O9/O10; two collected of 75 seen 18 November 1939, Abbott 1940; two seen 17 November 1956, AFN 11:61, 1957), Pacific Beach (Q7, on large lawn, no date, Sams and Stott 1959), Otay Mesa (V12/V13; up to 250 on 12 December 1971, G. McCaskie), Coronado Heights at the south end of the Silver Strand (U10/V10; five collected of 25 seen 1 January 1938, Abbott 1940), and the Tijuana River valley (regular 1962–91 with up to 201 on 18 December 1976, AB 31:882, 1972). In the last area the birds used both agricultural fields and the short grass around the airstrip at Ream Field (Imperial Beach Naval Air Station or Outlying Field; V10).
Migration: October to February was the Mountain Plover’s main season in San Diego County, with extreme dates in fall of 20 September (1972, 15 in the Tijuana River valley, G. McCaskie), in spring of 18 March (at Ocotillo Wells) and 3 April (1884, flocks seen—but no specimen collected—in Santa Ysabel Valley, I18/J18, Emerson 1887). The only report since 1991 is of a migrant at Stuart Mesa 19 October 1999 (P. A. Ginsburg, NAB 54:105, 2000).
Conservation: Abbott (1940) implied the Mountain Plover was already in decline by the late 1930s. On San Diego Christmas bird counts, the species was found in the Tijuana River valley almost annually from 1966, when the count circle was shifted to include the area, until 1979, when the count yielded 108. During the 1980s the numbers were much smaller, and the last report from the area was of five from 19 October through November 1991 (G. McCaskie, AB 46:149, 1992).