Figure 234. Orange County’s massive tern colony at Bolsa Chica has hosted a variety of exceptional vagrants, some of which have returned for multiple years. A case in point is this adult Sandwich Tern, pictured with Elegant Terns on 14 June 1997. This bird was believed responsible for all Sandwich Tern sightings at Bolsa Chica in 1991, 1995, 1996, and 1997. Nesting with an Elegant Tern was confirmed in 1995 and 1997. The subsequent appearance of a few apparent Sandwich × Elegant terns, both locally and elsewhere in the state, suggests that one or more of these attempts was successful (1997-100; Larry Sansone).

 

 

 

 

 

 

 

 

SANDWICH TERN Thalasseus sandvicensis (Latham, 1787)

Accepted: 3 (60%)	Treated in Appendix H: no
Not accepted: 2	CBRC review: all records
Not submitted/reviewed: 0	Large color image: see Figure

This tern maintains breeding colonies in Europe, along the Atlantic and Gulf coasts, and locally from the West Indies to southern Argentina. Northerly populations are migratory, and some birds winter on the Pacific coast from southeastern Oaxaca south to Ecuador and Peru. Atlantic vagrants are found rarely to casually north to the Maritimes and sometimes well inland in the East, usually associated with the passage of tropical cyclones. Relatively few vagrants have been recorded from the Pacific coast of Mexico, some of them with sparse supporting details; northernmost are sightings on 4 April 1987 from northern Sonora (Russell and Monson 1998) and 19 April 2003 from northeastern Baja California (NAB 57:407). Behaviors suggestive of breeding were observed during the 1990s on the Islas Marietas off the coast of Nayarit (Velarde et al. 2005) and on 19 February 2004 in Manzanillo, Colima (S. N. G. Howell in litt.). Far to the west in Hawaii, a bird was photographed 10–12 January 1992 (NAB:318, 333; dates fide R. L. Pyle).

The story of the Sandwich Tern’s occurrence in California begins with the Elegant Tern’s shifting status and distribution along the Pacific coast. Initially a breeding bird of the Gulf of California, the Elegant Tern in 1959 colonized San Diego Bay in San Diego County (Gallup and Bailey 1960). By the early 1980s that colony had stabilized at 600–860 pairs (Schaffner 1985). The species pushed northward again in 1987, settling in at Bolsa Chica in Orange County, where its numbers built to more than 1000 pairs by 1989 (Collins et al. 1991). This dramatic range expansion is correlated with increased stocks of the Elegant Tern’s primary prey, the Northern Anchovy (Engraulis mordax), off southern California (Schaffner 1986). An adult Sandwich Tern joined the San Diego Bay colony in 1980 (Schaffner 1981), 1982, 1985, and 1987. In June 1991, five weeks after an adult visited Malibu in Los Angeles County, what was possibly the same bird joined the Bolsa Chica colony. It was seen intermittently from 1991 to 1997, nesting with an Elegant Tern in 1995 and 1997 (Collins 1997; Figure 234). Sandwich Terns have lived for 16 to 23 years (Clapp et al. 1982 gave the lower figure, Terres 1980 the higher), so a single individual could have accounted for all of the California records.

Two adult terns showing bill characteristics intermediate between the Sandwich and Elegant were observed at Bolsa Chica during summer 1995 (Hamilton and Willick 1996). After reviewing photographs taken in July 1995 of an apparent hybrid Sandwich × Elegant Tern at the Pajaro River mouth in Monterey and Santa Cruz Counties, the late Claudia P. Wilds concluded that the bird was two years old; it may well have fledged at Bolsa Chica in 1993 (see Collins 1997). Hayes (2004) investigated intergradation between Sandwich (T. s. acuflavida) and Cayenne (T. s. eurygnatha) Terns in the Virgin Islands and published numerous photos of birds exhibiting intermediate bill coloration.