446 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



Females, wing 270-293 (282), tail 94-105 (99.7), culmen 30-34.5 

 (32.5), tarsus 39-41 (39.9), middle toe 31.5-34 (32.2) mm. 



Migrant from the north. Fairly common along both coasts ; 

 recorded on Gatun Lake. 



Adult Franklin's gulls, easily identified by the prominent black 

 and white markings on the end of the wing, are observed with fair 

 regularity among the hundreds of laughing gulls along the coasts, 

 but I have yet to detect one among the flocks that range the open 

 Gulf of Panama. It is probable that their pattern of migration is 

 like that of the related species, but at present there is no definite 

 infoiTnation on this. Some nonbreeding individuals remain in 

 Panama through the period of northern summer. They are seen 

 occasionally on Gatun Lake, but have not been recorded elsewhere 

 in the interior. 



The only specimen I have examined is an immature bird in the 

 U. S. National Museum, taken at Panama City by Dr. George 

 Suckley, on December 28, 1855. There is a further record of one 

 banded in South Dakota in June 1940 that was found on the Pacific 

 coast of Panama in the vicinity of the Golfo de Montijo on July 8 of 

 the following year. In my own observations I have seen these birds at 

 Panama Viejo, recording 15 to 20 on December 28, 1955, one at the 

 Miraflores Locks December 29, 1963, and have found an occasional 

 one among the many laughing gulls at Fort Amador. 



CREAGRUS FURCATUS (N6boux): Swallow-tailed Gull; 

 Gaviota Rabihorcado 



Larus furcatiis Neboux, Voy. "Venus," Atlas, Zool., Ois., 1846, pi. 10. 

 (Galapagos Archipelago.) 



A large, gray-backed gull, with dark head, and forked tail. 



Description. — Length 550 to 600 mm. Tail deeply forked. Adult, 

 in breeding dress, head and neck slate gray, with a white spot on the 

 forehead at the base of the bill, and a smaller one on the feathers 

 adjacent to the side of the lower mandible ; back, rump, and lesser 

 wing coverts gray, with the scapulars edged with white ; outer webs 

 of primaries black; inner webs, rest of wing coverts, secondaries, 

 and tail white; sides of breast and lower foreneck pale gray; rest 

 of under surface white. 



Nonbreeding dress, head white, streaked with gray; space around 

 eyes and over ears grayish black. 



Immature, brown above; head white streaked as in nonbreeding 

 dress of adult ; below white. 



