Figure 116. This classic American × Black Oystercatcher, an adult showing extensive dusky mottling on the underparts, was photographed on 4 February 1997 at Royal Palms Park on the Palos Verdes Peninsula, Los Angeles County (1997-045; Don DesJardin).

 

Figure 220. Two of three first-fall American Oystercatchers present at the Salton Sea from 14 to 30 August 1977—the state’s only interior record. This photograph was taken on 24 August, after the birds had flown from Salton City in Imperial Couny to an area between North Shore and Salt Creek in Riverside County (1977-085; Jeri M. Langham). These birds probably originated in the Gulf of California, where subspecies frazari is resident. They appear “cleaner” below than is typical of frazari on the Pacific coast, where Black Oystercatchers have tainted the gene pool. Nominate palliatus from the East cannot be ruled out entirely (see Patten et al. 2003).

 

 

 

 

 

 

AMERICAN OYSTERCATCHER Haematopus palliatus Temminck, 1820

Accepted: 26 (52%)	Treated in Appendix H: yes
Not accepted: 24	CBRC review: all records
Not submitted/reviewed: 32 (many apparent hybrids)	Large color image: see Figures

This shorebird occurs along the Pacific coast from northwestern Baja California to central Chile, and along the Atlantic coast, primarily from southern Maine to south-central Argentina, including islands off both coasts. Most populations are resident, but northerly birds—especially those in the Northeast—migrate south in winter. The species is generally accidental in the continent’s interior, east of the Rocky Mts., with most records associated with the passage of tropical cyclones. Outside of California, the only records from the interior West consist of a sight report for Idaho (Stephens and Stephens 1987) and a possibly acceptable record from New Mexico (Williams 2000, cf. AOU 1998).

An adult female American Oystercatcher collected on 16 May 1862 in San Diego, San Diego County, was California’s first (Cooper 1868). A year later, on 2 June 1863, a female with a fully developed egg in its oviduct was collected at Santa Barbara Island, Santa Barbara County (Cooper 1870). California’s coastal records involve H. p. frazari of western Mexico. Jehl (1985) found that American and Black Oystercatchers frequently hybridize where their ranges overlap along the northern Pacific coast of the Baja California Peninsula. Considerable gene flow between these taxa appears responsible for the somewhat variable plumage of frazari in this part of the range. Jehl’s plumage scoring system (see below) suggests quantifiable phenotypic parameters for both species while allowing birds within each species to show some intermediate characters. Committee members have considered the possibility of hybridization for all records, although the issue has undoubtedly been taken more seriously since Jehl’s frequently cited work (see Patten and Erickson 1994, Erickson and Terrill 1996).

Although both Jehl and the CBRC concluded that neither of the state’s first two specimens are hybrids, Roberson (1993) noted that three different people assigned scores of 26, 27, and 29 to the 1863 specimen—values at the upper end of Jehl’s hybrid range (10–29). Jehl himself scored the specimen a 27, exemplifying the predicament faced by anyone attempting to judge the acceptability of borderline individuals. Unsurprisingly, CBRC members have likewise been unable to develop a uniform “standard of purity” for Pacific coast frazari. Nevertheless, a number of birds have been judged to be definite hybrids, including one present from 18 January to 15 February 1997 on the Palos Verdes Peninsula, Los Angeles County (Figure 116); see also the 9 June 2001 photograph of an apparent hybrid on Santa Cruz Island, Santa Barbara County (NAB 55:356); also Wehtje (2005). As noted in the record table, some accepted records involve birds that showed intermediate characters.

The state’s only inland record, and the most thoroughly documented record from the interior West, refers to three first-fall birds present 14–19 August 1977 at Salton City in Imperial County and 20–30 August 1977 across the Salton Sea, in the area between North Shore and Salt Creek in Riverside County. As shown in Figure 220, these birds showed relatively sharp breast divisions, clean white bellies, and no dusky flank markings. Birds ascribed to frazari in the Gulf of California have no opportunity to mingle with Black Oystercatchers, and this shows in their relatively “clean” appearance (compared with frazari from the zone of overlap). Patten et al. (2003), however, raised the possibility that the Salton Sea birds may have represented nominate H. p. palliatus, which occurs no closer than the Gulf coast of Texas.

The Channel Islands account for about three out of every five accepted records of this species in California (16 of 26); see also Appendix H. A number of birds have taken up residence on these islands, including two individuals thought to persist for at least 17 years: one on Anacapa Island in Ventura County and the other on Santa Cruz Island in Santa Barbara County. Records of first-year birds and apparent family groups on some islands suggest occasional breeding and possibly more frequent interbreeding (e.g., Sullivan and Kershner 2005:261, Wehtje 2005). Numerous unpublished Channel Island records of potentially acceptable American Oystercatchers, as well as evident hybrids, have never been submitted for CBRC review (fide P. W. Collins).

 

[PIED AVOCET Recurvirostra avosetta Linnaeus, 1758 – see hypothetical section]

 

A Scoring System for Assessing the Intermediacy
of Black and American Oystercatchers

This system was originally published by Jehl (1985, Table 1). Jehl generally considered birds with total scores (all characters added together) from 0 to 9 to be Black Oystercatchers (H. bachmani), from 10 to 29 to be hybrids, and from 30 to 38 to be American Oystercatchers (H. palliatus). The system was devised for use with specimens; some characters may be difficult or impossible to score under normal field conditions.

Character State		Score
Upper tail coverts
	Black, as in bachmani	0
	Black, a few white mottlings	1
	Nearly equally black and white	2
	White, a few black mottlings	3
	White, as in palliatus	4
Tail
	Black, as in bachmani	0
	Mainly black, trace of white at base of vanes	1
	Basal quarter of rectrices white	2
	Basal third of rectrices white	3
	Basal half of rectrices white, as in palliatus	4
Chest
	Black, with black chest band extending smoothly onto midbelly, as in bachmani	0
	Black chest band extending onto upper third of belly	1
	Black chest band extending onto upper quarter of belly	2
	Black chest band bordered by ragged edge on upper breast	3
	Black chest band sharply delimited from white of upper chest, as in palliatus
Belly
	Blackish, as in bachmani	0
	Blackish, with traces of white on a few feathers	1
	Blackish, white area around crissum	2
	Three quarters black, one quarter white	3
	Nearly equally black and white	4
	Three quarters white, one quarter black	5
	Entirely white, as in palliatus	6
Under tail coverts
	Entirely black, as in bachmani	0
	Mainly black with slight white mottling	1
	Nearly equally black and white	2
	Mainly white	3
	Entirely white, as in palliatus	4
Thighs
	Entirely black, as in bachmani	0
	Black with grayish underdown, not noticeable externally	1
	Puffs of grayish down noticeable	2
	Mainly white	3
	Entirely white, as in palliatus	4
Greater secondary coverts (width of white edging in folded wing)
	White lacking, as in bachmani	0
	Less than 2 mm	1
	2–5 mm	2
	6–15 mm	3
	Greater than 15 mm	4
Extent of white wing stripe
	White lacking, as in bachmani	0
	White markings confined to inner half of secondaries	1
	White markings extend to outer secondaries only	2
	White present on some or all of inner five primaries	3
	White present on at least one of primaries 6–10	4
Underwing coverts
	Entirely black, as in bachmani	0
	Mainly black, some white mottling	1
	Nearly equally black and white	2
	Mainly white	3
	White, as in palliatus	4
Axillars
	Black, as in bachmani	0
	Mainly black, some white mottling	1
	Nearly equally black and white	2
	Mainly white	3
	White, as in palliatus	4