Black-necked
Stilt
Himantopus mexicanus
The
comical Black-necked Stilt is a common year-round resident of shallow
lagoons and ponds along San Diego County’s coast.
It avoids tidal mudflats but uses some inland lakes and ponds—especially
sewage ponds. The salt works of
south San Diego Bay are by far the stilt’s primary site in San Diego County,
hosting a third to a half of the approximately 1000 stilts wintering in
the county. The stilt apparently colonized the county as
a breeding species in the 1930s and 1940s; by the beginning of the 21st
century it was about as abundant in summer as at other seasons.
Breeding
distribution:
The ponds of the south San Diego Bay salt works (U10/V10) offer the stilt
ideal foraging habitat, while the dikes offer ideal nest sites. On their weekly surveys of the salt works through
spring and summer 1993, Stadtlander and Konecny (1994) found close to
200 stilts, and in summer 1997 Michael R. Smith estimated 100 nests. In the
Breeding stilts are also fairly widespread
inland, though generally uncommon. There they occur mainly in the coastal
lowland and especially in the valleys of the lower Santa Margarita and
San Luis Rey rivers, where there are many ponds. Fifty at a pond Siempre Viva and La Media roads,
Otay Mesa (V13), 12 June 2001 (P. Unitt) and 24 (including juveniles)
at ponds at the west end of Santa Maria Valley (K13) 14 July 2000 (P.
M. von Hendy) are high inland counts for the breeding season.
At 1300–1400 feet elevation, the most inland sites we confirmed
stilt breeding were the last location, sewage ponds at the base of Spangler
Peak in San Vicente Valley (L15; 12 on 6 June 2000, A. Mauro), and Barona
Valley (N15; six, including young, on 16 July 2001, J. Smith). But the species may breed also at Lake Henshaw
(G17; up to four on 18 June 2000, P. Unitt), the upper end of Lake Morena
(S22; up to 12 on 2 July 2000, R. and S. L. Breisch), and Tule Lake (T27;
up to four on 6 June 2001, J. K. Wilson).
Nesting: The Black-necked Stilt
nests on the ground, sometimes amid low vegetation, sometimes in the open,
as on the dikes of sewage ponds or the salt works.
If there is loose debris around the nest, the birds gather it around
the eggs. The adults call constantly
and feign injury and incubation as an intruder approaches the nest, driving
birders as well as predators to distraction.
Our dates for nests with eggs or incubating adults ranged from
15 April to 18 July.
Migration: Information on stilt movements
in San Diego County is contradictory, perhaps because of changes in habitat
use by season and the irregularity of water levels attractive to the birds.
Unitt (1984) reported the species most abundant in fall migration,
peaking in August. At Lake Hodges K. L. Weaver noted a maximum
of 30 on 3 August 1985. At San
Elijo Lagoon, King et al. (1987) found the stilt most common from June
to September, least common from November to March.
In the salt works, Stadtlander and Konecny (1994) found the numbers
maintained from February to August 1993 increasing to a higher level from
September 1993 to February 1994.
At ponds in the Borrego Valley the
stilt is a rare migrant, recorded from 28 March (P. D. Ache) to 12 May
in spring, from 31 July to 22 September in fall (ABDSP database). Numbers there are usually small; the maximum
is of 25 at the Borrego sewage ponds (H25) 25–26 April 1987 (A. G. Morley).
Winter: The stilt’s distribution in winter is quite similar
to that during the breeding season. In
the salt works, Stadtlander and Konecny (1994) found up to 685 on 9 February
1994; during the atlas period, our maximum there was 253 on 19 December
1998 (D. C. Seals et al.). Along
the north San Diego County’s coast, where the stilt becomes less abundant
in winter, our high counts were of 40 in the Santa Margarita River estuary
(G4) 10 December 1999 (P. A. Ginsburg), 39 at sewage ponds near there
(G5) 6 December 1998 (R. E. Fischer), and 80 at San Elijo Lagoon 22 December
2000 (G. C. Hazard). Numbers inland
ranged up to 30 at Whelan Lake (G6) 23 December 2000 (D. K. Adams) and
41 at Siempre Viva and La Media roads 29 December 2000 (P. Unitt).
From
1997 to 2002 our winter records farthest inland were of one in Ballena
Valley (K17) 15 January 1999 (D. C. Seals) and three on the north side
of Lake Morena (S21) 24 February 2002 (R. and S. L. Breisch).
The species has been found once on a Lake Henshaw Christmas bird
count, with two on 19 December 1994, and once on an Anza–Borrego Christmas
bird count, with one on 31 December 1988.
Conservation: The Black-necked Stilt
was first found nesting in San Diego County in 1931 (Willett 1933); previously
it was known as a migrant only (Stephens 1919a). Creation of the salt works undoubtedly increased
the stilt’s numbers greatly, and the installation of sewage ponds and
reservoirs added new sites. Kenneth
L. Weaver suspected nesting inland at
Taxonomy: The classification of the
world’s stilts has varied, but the current practice (A. O. U. 1998) is
to group the subspecies of the New World, including that of Hawaii, under
Himantopus mexicanus (Müller, 1776).
The nominate subspecies occurs throughout North America.
American
Avocet
Recurvirostra americana
The
American Avocet’s primitive habitat is shifting shallow wetlands, which
it sweeps for aquatic invertebrates. In
spite of the loss of much of this habitat, the avocet remains locally
common in San Diego County by taking advantage of salt ponds, sewage ponds,
and partially blocked lagoons. Once
considered just a migrant in San Diego County, the avocet now occurs year
round. Though it nests on the ground, the avocet often
enjoys success, with the help of its screaming and strafing of any approaching
predator.
Breeding
distribution:
From 1997 to 2001, Batiquitos Lagoon was the center of avocet abundance
in San Diego County, with up to 184 adults in the east basin (J7) 3 April
1998 (F. Hall) and 36 nests within one Least Tern colony in 2001 (S. M.
Wolf). The species occurred in all the other wetlands
of coastal northern San Diego County, however, from Aliso Creek (F4) to
Los Peñasquitos Lagoon (N7), with nesting confirmed at almost all of these.
Also, small numbers nest at several sites up to 8 miles inland
in the valleys of the Santa Margarita and San Luis Rey rivers.
Along the county’s south coast known nesting sites are Famosa Slough
(R8; nest 25 April–7 May 1997, J. A. and B. J. Peugh), the south San Diego
Bay salt works (U10/V10; 40 nests estimated in 1997, M. R. Smith), Camp
Surf along the beach just north of Imperial Beach (V10; nest 22 April
2001, T. Stands, S. Yamagata), the Tijuana River estuary (V10/W10; five
nests 22 April 1997, B. Peterson), and inland in the Tijuana River valley
(W11; pair in distraction display 19 June 1999, P. Unitt).
We also found avocet nesting at several
scattered sites well inland. The
largest number of birds were at Lake Henshaw (G17; up to 30, some in distraction
display, 18 June 2000, P. Unitt), the east end of Lake Hodges (K11; up
to 40, including young, 9 June 1997, E. C. Hall), and the pond at Siempre
Viva and La Media Roads, Otay Mesa (V13; up to 20, including young, 12
June 2001, P. Unitt). Some other
sites, such as a sewage pond near the Barona Casino (N14), had just an
isolated pair (nest 29 June 1997, P. R. Pryde).
All of these sites are on the coastal slope except for one on the
Campo Plateau at Tule Lake (T27; six on 21 June 2000, J. K. Wilson).
Nesting: Sometimes avocets nest
in shallow depressions with no nesting material whatever. The birds apparently nesting on extensive flats
devoid of vegetation on the north side of Lake Henshaw were in such a
situation. Often, however, as in
marshes of pickleweed, they build a substantial platform of debris. Our dates for avocet nests ranged from 20 April
to 29 June, with one already with four eggs in the salt works 1 April
1997 (M. R. Smith).
Migration: The seasonal pattern of
avocet abundance in San Diego County varies from site to site with variations
in water levels, which may mask the evidence of large-scale migrations. On the basis of monthly counts at San Elijo
Lagoon (L7) 1973–83, King et al. (1987) found the avocet’s average abundance
peaking in March and April, relatively low from August to January. Yet their maximum count was in December. On the basis of weekly counts in the salt works
February 1993–February 1994, Stadtlander and Konecny (1994) found avocet
abundance peaking in winter, with a maximum count of 467 in January, then
falling to an average of about 25 from May to August. In the Anza–Borrego Desert, where the avocet
is a rare visitor, records range from 11 September (1982, 12 at Middle
Willows, C22) to 12 May (1974, three at Bow Willow Ranger Station, P28,
ABDSP database). None was found
there during the atlas period. Indeed,
from 1997 to 2002, atlas observers saw almost no avocets far from sites
of likely breeding.
Winter: In winter the avocet is
concentrated at the same coastal wetlands where it nests. During the atlas period the primary sites were
Batiquitos Lagoon (up to 210 on 2 January 1998, C. C. Gorman), San Elijo
Lagoon (up to 600 on 23 February 1997, A. Mauro), and the old sewage ponds
and gravel pits now reintegrated into the Tijuana estuary (up to 197 on
18 December 1999 (R. B. Riggan). Inland,
the major site by far is Lake Hodges, with up to 70 on 9 December 1997
(E. C. Hall). We did not find the avocet in winter at several
inland sites where we found it during the breeding season. Our only winter records outside the coastal
lowland were from the upper end of Lake Morena (S22; one on 5 December
1999, R. and S. L. Breisch) and Lake Henshaw (noted on 5 of 22 Lake Henshaw
Christmas bird counts 1981–2002, with up to six on 19 December 1994 but
no more than two 1997–2002). The
Anza–Borrego count has recorded the avocet only once, a flock of 19 on
17 December 1995.
Conservation: The American Avocet has
lost considerable habitat throughout its range, including southern California.
But the establishment of the salt works, reservoirs,
and sewage ponds created new habitat in San Diego County, probably increasing
what was available under primitive conditions. The avocet’s colonizing the county as a breeding
species evidently began in the 1950s (Sams and Stott 1959). By the 1970s the birds were not yet nesting
regularly in the salt works (Unitt 1984).
Their nesting inland in the county was first confirmed in 1982
with five pairs at Lake Hodges 19 June (K. L. Weaver).