438 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



Measurements (from Ridgway, I.e., p. 696). — Males, wing 295- 

 327 (309.1), tail (to end of middle rectrices) 263-350 (299), culmen 

 27-31.5 (28.6), tarsus 38-44 (41.1) mm. 



Females, wing 305-317 (313.3), tail (to end of middle rectrices) 

 238-350 (295), culmen 27.5-30 (28.8), tarsus 40-42.5 (41.8) mm. 



Visitor from the north. Status not certain. 



The only record is of one seen by L. Griscom and M. Crosby in 

 Colon harbor on February 9, 1927 (Griscom, Amer. Mus. Nov. no. 

 282, 1927, p. 3). 



Adults of the two smaller jaegers usually may be separated on the 

 length of the central tail feathers ; and a small bird in dark phase 

 plumage may be accepted as 6*. parasiticus, since this type of colora- 

 tion in 5. longicaudus is not yet firmly established by a specimen. 

 Field identification of immature individuals is uncertain unless 

 chance may give a clear view of the leg color, black in parasiticus and 

 bluish gray in longicaudus. With birds in the hand the two may be 

 separated by close scrutiny of the size of the bill — heavier in para- 

 siticus, slightly more slender in longicaudus. It is probable that both 

 species come occasionally along the coasts so that I have included 

 them on the basis of sight records, which are not wholly certain. 



Family LARIDAE : Gulls and Terns ; Gaviotas y Gaviotines 



The two groups of aquatic habit included in this family, while 

 allied structurally, differ so clearly in carriage and action that they 

 are distinguished at a glance by any one reasonably familiar with 

 them. The gulls are larger and are more robust, wider-winged birds 

 that in flight carry the strong, rather heavy bill with its hooked tip 

 pointed forward in line with the long axis of the body. While they 

 may snatch at food on the surface of the water, it is not their 

 regular habit to dive. All the species found in Panama are migrant 

 from the north or south. Terns as a group are small, with slender 

 bodies, and narrow, pointed wings. As they fly over the water in 

 search of food the slender, straight bill is pointed down at an angle, 

 and the birds habitually feed by plunging, often going beneath the 

 surface. Only the royal tern, of those found in Panama, has the 

 body size of the smaller gulls. At least two species, the noddy and 

 the sooty tern, come to nest on the rocky islets of Los Frailes off 

 Punta Mala. Probably a third, the bridled tern, may breed there also. 

 Other kinds are found as migrants. While both gulls and terns range 

 along the coasts, some of them come inland on larger bodies of fresh 

 water. 



