• Corpus ID: 54621854

HYBRIDIZATION OF A SANDWICH AND ELEGANT TERN IN CALIFORNIA

@inproceedings{Collins1997HYBRIDIZATIONOA,
  title={HYBRIDIZATION OF A SANDWICH AND ELEGANT TERN IN CALIFORNIA},
  author={Charles T. Collins},
  year={1997}
}

• C. T. Collins
• Published 1997
• Environmental Science

The Sandwich Tern ($terna sandvicensis) is a widespread breeding species on the Atlantic coasts of Europe and North America (AOU 1983, Cramp 1985) and the Caribbean (AOU 1983). On the Pacific coast it winters south to Colombia (Hilty and Brown 1986), Ecuador (Ridgely 1981), and Peru (Junge and Voous 1955, Harrison 1983). Although the Sandwich Tern is a "common transient and winter resident" in Panama (Ridgely 1981), it is decidedly less common farther south. Sandwich Terns also occur sparingly in winter northward on the Pacific coast of Central America as far as Oaxaca, Mexico (Peterson and Chalif 1973, AOU 1983). Since there are no recorded breeding colonies on the Pacific coast it is assumed that all Sandwich Terns on the Pacific coast of Central and South America represent wintering migrants from Ariantic or Caribbean colonies. The recovery in Buenaventura, Colombia, of a Sandwich Tern that had been banded in a breeding colony in North Carolina (Hilty and Brown 1986) supports this view. In California, the Sandwich Tern is considered "accidental" (Unitt 1984) or "exceedingly rare" (Small 1994); as argued below, all records may pertain to only two individuals. The first Sandwich Tern in California was observed in May 1980 on the dikes around salt-evaporation ponds in south San Diego Bay near Imperial Beach (McCaskie 1980, Schaffner 1981, Luther et al. 1983). This bird was seen with a fish in its bill, approaching Elegant Terns (Sterna elegans) nesting there. It was in the typical stance of a male courting a female. In all cases observed, this presumed male was driven off by the Elegant Terns (Schaffner 1981). What was considered to be the same individual was seen in San Diego Bay 15 May-13 June 1982 (McCaskie 1982a,b, Morlan 1985), 12-14 June 1985 (Bevier 1990), and 18 April-16 May 1987 (Langham 1991). There was no suggestion of breeding by this Sandwich Tern in any year, and it was not seen again after 1987. On 20 May 1991 an adult Sandwich Tern was observed at Malibu Lagoon, Los Angeles County, by Barbara Elliott (pers. comm.). A single Sandwich Tern also was observed on 29 June 1991 among nesting Elegant Terns at Bolsa Chica Ecological Reserve, Orange County, by Brian Daniels and Doug Willick (pers. comm.). The bird observed at Malibu Lagoon was reported to be in alternate plumage and the one at Bolsa Chica in basic plumage, suggesting to some that two individuals were present in 1991 (Patten et al. 1995). The Malibu bird was described as having a cap "black from bill to nape" (Elliott in litt.), typical of an alternate-plumaged adult. The Bolsa Chica bird "showed a considerable amount of white [on the head] espedally anteriorly" (Willick in litt.), as was also true of many of the Elegant Terns on this date. This indicates the start of the prebasic molt; the bird was not in the full basic plumage. The interval between these separate observations (40 days) was more than sufficient for the prebasic molt to have begun and for many of the black forehead feathers to have been replaced by white ones, as observed in many Elegant Terns by this date (pers. obs., Figures 1-2). Thus, ! agree with McCaskie (1991), who suggested that the Sandwich Terns seen at Malibu and Bolsa Chica in 1991 were the same individual. At Bolsa Chica on 24 June 1995 my attention was drawn by Robert Schallmann and Tom Ryan to a tern with a yellow-tipped black bill among the Elegant Terns nesting there. Closer examination showed that not only was it an adult Sandwich Tern but it was attending a nest. While we watched at ranges of <20 feet, this bird was seen