Figure 161. Among California’s most controversial records was that of an adult Swallow-tailed Gull present 6–8 June 1985 in Pacific Grove and Moss Landing, Monterey County. It was photographed at the former locale on 7 June 1985 (1985-079; Peter LaTourrette).

 

 

 

 

 

 

SWALLOW-TAILED GULL Creagrus furcatus (Néboux, 1842)

Accepted: 2 (100%)	Treated in Appendix H: no
Not accepted: 0	CBRC review: all records
Not submitted/reviewed: 1	Color image: none

This unique gull breeds in the Galapagos Islands and on Malpelo Island off Colombia. Dispersal is generally southward into the Peru Current from Ecuador south to north-central Chile. The AOU (1998) cast doubts on earlier reports from Panama (Robins 1958, Reed 1988), but in recent years multiple birds have been documented in waters off Panama and Costa Rica, including counts of up to three birds far off the coast of Costa Rica between 30 April and 5 May 2006 (NAB 60:452, 454). Records at sea up to 1200 nautical miles from the Galapagos Islands (fide L. B. Spear) further demonstrate this gull’s capacity for long-distance dispersal.

The appearance of an adult Swallow-tailed Gull in Monterey County during early June 1985 spurred debate about the bird’s natural occurrence (FN 50:328, Heindel and Garrett 1995; Figure 161). Roberson (1985, 2002) attributed its appearance in central California to lingering effects of the 1982/1983 El Niño, one of the strongest on record (Rasmusson 1985). This disruptive phenomenon apparently forced Swallow-tailed Gulls out of the Peru Current (Arntz 1986, see Veit 1985) and was implicated in the occurrence of this species and Inca Terns (Larosterna inca) in the Bay of Panama (Reed 1988). Furthermore, it is thought that the Swallow-tailed Gull’s small population size, inaccessible breeding sites, and strongly pelagic and nocturnal habits (see Belopolsky and Tsigankova 1985) make it an unlikely captive. After considerable debate, with input from numerous seabird experts, the Committee decided to await additional records, either from California or from geographically intermediate regions.

In March 1996, a second Swallow-tailed Gull appeared in California, at sea west of Southeast Farallon Island. The second record followed a protracted period of elevated sea surface temperatures in the eastern Pacific Ocean between 1991 and 1995 (National Oceanographic and Atmospheric Administration data). The Committee re-evaluated the 1985 record in light of this additional occurrence, ultimately accepting both records. The checklist committees of the AOU (1998 and supplements through 2006) and ABA (2002; Robbins et al. 2003–2006) have yet to accept the Swallow-tailed Gull to their lists of naturally occurring North American birds.