II SPECIES ACCOUNTS Andy Birch PDF of Wood Stork account from: Shuford, W. D., and Gardali, T., editors. 2008. California Bird Species of Special Concern: A ranked assessment of species, subspecies, and distinct populations of birds of immediate conservation concern in California. Studies of Western Birds 1. Western Field Ornithologists, Camarillo, California, and California Department of Fish and Game, Sacramento. California Bird Species of Special Concern WOOD STORK (Mycteria americana) Kimball L. Garrett Criteria Scores Population Trend 10 Range Trend 20 Population Size 10 Range Size 10 Endemism 0 Population Concentration 10 Threats 10 Current Postbreeding Range Historic Postbreeding Range County Boundaries Water Bodies Kilometers 80 40 0 80 Current and historic (ca. 1944) postbreeding range of the Wood Stork in California; numbers have always fluc- tuated considerably from year to year, and individual birds occasionally wander far north of the mapped range. Formerly, the greatest numbers were at the south end of the Salton Sea and adjacent Imperial Valley, and many fewer were on the coastal slope of southern California and in the lower Colorado River valley. Now found in very small numbers only at the southern end of the Salton Sea. Wood Stork Studies of Western Birds 1:143–148, 2008 143 Studies of Western Birds No. 1 SPECIAL CONCERN PRIORITY California, occurring almost exclusively from late May to mid-September (very rarely early Apr to Currently considered a Bird Species of Special late Nov; Garrett and Dunn 1981, Patten et al. Concern (postbreeding), priority 1. Included on 2003). Lower Colorado River records since 1974 CDFG’s (1992) unprioritized list but not on the have been between 9 June and 30 September original prioritized list (Remsen 1978). (Rosenberg et al. 1991). In San Diego County, formerly occurred irregularly in large numbers BREEDING BIRD SURVEY STATISTICS from July through September, with some as early FOR CALIFORNIA as late May (very rarely Mar–Apr) and a few lin- Data inadequate for trend assessment (Sauer et gering to December and January (Unitt 2004). al. 2005). HISTORIC RANGE AND ABUNDANCE GENERAL RANGE AND ABUNDANCE IN CALIFORNIA A subtropical and tropical wading bird with a Historically, the Wood Stork occurred annually wide distribution from Mexico and the extreme as a nonbreeding visitant to southern California. southeastern United States south through much Principal areas of occurrence included the coast of lowland South America (generally east of the (mainly north to Ventura County), the Imperial Andes; Blake 1977, Howell and Webb 1995). No Valley and Salton Sea, and the lower Colorado subspecies recognized. Within the United States, River valley north to Needles, San Bernardino breeding generally limited to peninsular Florida County (Abbott 1931, 1935; Grinnell and Miller (very local in the Panhandle), Georgia (mainly 1944). Numbers and areas occupied were variable, coastal plain, but local in southwest), and extreme with abundance and regularity greatest in Imperial southern coastal plain of South Carolina; formerly County (Abbott 1935, 1938), but overall storks bred in Texas, Alabama, and Louisiana (Coulter were considered “locally common” (Grinnell and et al. 1999). Isolated nesting attempts recorded Miller 1944). in California (see below). In western Mexico, In the Salton Sea area, Wood Storks occurred Wood Storks nest north to Sinaloa, but numbers almost exclusively as postbreeding visitors; num- have declined in the northern part of the range bers varied from year to year, but the species (Russell and Monson 1998). The species remains was often “fairly common to abundant” (Patten a “fairly common to common” resident and local et al. 2003). In 1938, a year of “exceptional breeder in the remainder of its Mexican range, influx,” Abbott (1938) reported a high count of from Sinaloa and Tamaulipas southward (Howell 1500–2000 storks in an alfalfa field one mile east and Webb 1995). Knoder et al. (1980) recorded of Seeley, Imperial County, on 7 and 17 August. breeding colonies of up to 500 nests in several Stork occurrences on the coast were more irregu- coastal localities from Guerrero to Chiapas. The lar, but in some years (e.g., 1923, 1934, 1938) largest breeding colonies in Mexico are in the “notable invasions” occurred (Abbott 1935, 1938; southern Gulf of Mexico coast from southeastern Unitt 1984). Along the lower Colorado River, Veracruz to central Campeche, where Sprunt early observers considered storks “common to (1980) estimated some 15,000 breeding pairs. abundant” (Rosenberg et al. 1991), and some Irregular northward postbreeding dispersal to birds perhaps occasionally remained through the the southwestern, Gulf coast, and southern Atlantic winter and spring (e. g., flocks reported in Jan states; small flocks or individuals occasionally through Apr). Storks ranged north rarely to the occur as vagrants far to north of these regions, with Bill Williams River delta on the Arizona side of great interannual fluctuations in numbers (Lowery the river. 1974, Coulter et al. 1999). Postbreeding numbers Formerly, the Wood Stork was “irregularly have declined in southern California (see below) common” in coastal lagoons of San Diego County and in the adjacent Mexicali Valley and Colorado from July to September (Unitt 1984, 2004), with River delta region of Mexico (Ruiz-Campos and maxima including “hundreds” in the Sweetwater Rodriguez-Meraz 1997, Patten et al. 2001). River Valley near Dehesa 30 August 1923 and 500 at Agua Hedionda Lagoon 1–14 August 1938 (Abbott 1931, 1938). Unitt (1984) emphasized SEASONAL STATUS IN CALIFORNIA the great interannual fluctuations in numbers Apart from extralimital nesting in San Diego in San Diego County. The species was probably County, currently a postbreeding visitor to “regular” in coastal Orange County through the 144 Species Accounts California Bird Species of Special Concern mid-20th century (Hamilton and Willick 1996), Along the lower Colorado River, the largest with up to 30 at Balboa in August 1934 (Abbott flock recorded was 230 birds on 16 July 1959 near 1935), but few specific records exist. Flocks of 25 Laguna Dam, Imperial County (Rosenberg et al. or more birds were found in coastal Los Angeles 1991); maximum concentrations in the 1980s in County in the early 20th century (Willett 1912). that region (at Cibola NWR, just across the border Numerous records come from further north, in in Arizona), were of 10–50 birds (Rosenberg et al. Ventura, Santa Barbara, and San Luis Obispo 1991). There are few records for the California counties, where storks were decidedly uncommon side of the river since the 1970s. and irregular (Marantz 1986, Lehman 1994). Coastal occurrences were always erratic, but Wood Storks were not restricted to the immedi- years of occurrence dropped steeply after about ate coast. Grinnell (1898) cited an observation of 1960 and have today declined to near zero. In San “a large flock on the barley fields” near Claremont, Diego County, where storks were formerly most Los Angeles County, in June 1897, and Willett numerous, the last large concentration reported (1912) cited records along the Santa Ana River was of 300 birds at Buena Vista Lagoon in in Riverside (date unspecified) and near San July and August 1953 (Unitt 2004); occurrences Bernardino in the summers of 1891 and 1902. declined greatly through the 1950s, with the last Illustrating the propensity of this species to wan- substantial flocks noted in 1961 (Unitt 1984). A der, records extended north to Alameda County single pair attempted to nest near Imperial Beach on the coast and in the interior to Inyo, Fresno, in the spring 1987, and what may have been the Merced, Siskiyou, and Modoc counties (Grinnell same pair nested in a heronry within the San and Miller 1944, McCaskie et al. 1988). Diego Wild Animal Park in San Pasqual in 1989 and 1991 (Unitt 2004). In all these attempts RECENT RANGE AND ABUNDANCE eggs were laid but did not hatch. One individual IN CALIFORNIA remained in the colony at the Wild Animal Park as of 2003 (Unitt 2004). Storks were last recorded Currently, Wood Storks in California are almost in Orange County when up to five were found entirely limited to the southeastern portion of the on 8–9 September 1971 (Hamilton and Willick Salton Sea (see map). They remained numerous at 1996); there are no records for Los Angeles the Salton Sea until the 1970s (Patten et al. 2003, County since February 1982 (Long 1993). The 2004) and experienced a steep decline thereafter. most recent record for Santa Barbara County, Numbers on the coast apparently declined greatly where storks apparently were always rare, was 5 after the early 1950s, and only occasional individ- June to 1 August 1983 at Sandyland Slough in uals were recorded after the 1960s (Unitt 2004). Carpinteria (Lehman 1994). There is one recent For the Salton Sea, few quantitative data exist vagrant record for Monterey County (10–31 Jul prior to the 1960s. Patten et al. (2003) cited a 1976 in Big Sur; Roberson 2002). flock of 2000 at the south end of the Salton Sea on 18 July 1974, and Garrett and Dunn (1981) ECOLOGICAL REQUIREMENTS noted high counts there of 1000 birds on 18 September 1964 and 650 birds in late July 1977; At the Salton Sea, Wood Storks forage in shallow these are the last years in which such large con- bays, marshy backwaters, canals, and drains, being centrations occurred. The great majority of birds most numerous around the mouths of the New at the Salton Sea have concentrated at the south and Alamo rivers (Garrett and Dunn 1981), espe- end, in Imperial County (Garrett and Dunn cially the latter in recent years (Patten et al. 2003). 1981); the species is scarce at the north end, in Resting and roosting birds use partly submerged Riverside County (about 10 records, generally of trees and shrubs in backwater areas or large snags single birds; Patten et al.