FAMILY RYNCHOPIDAE 463 



the birds were at a distance, there is no question that those near at 

 hand are brown noddy terns. It is also evident that they seemed to 

 be at a nesting ground. It appears, therefore, that in addition to the 

 sooty terns that I found at Los Frailes del Sur, two other species, 

 the bridled tern and the brown noddy, may come to breed on these 

 two groups of rocks. 



The records cited are placed under the name ridgwayi in accordance 

 with current usage. No specimens from Panamanian waters are 

 available, but those that I have examined from Cocos Island appear 

 darker over the body and darker gray on the crown than our series 

 from along the west coast of Mexico that represent the typical popu- 

 lation of ridgwayi. In fact, the few seen from Cocos in darker color 

 show a definite approach to the race galapagensis that nests at the 

 Galapagos. Birds from Clipperton Island to the north of Cocos also 

 are somewhat different from the Mexican series. 



Murphy (Nat. Hist., vol. 41, 1938, p. 177) has reported many 

 brown noddies around Cabo Marzo and Octavia Rocks on the coast 

 of Colombia, a short distance south of boundary with Panama, and 

 there is record of one taken at Isla de Malpelo, Colombia. In the 

 collections of the British Museum (Natural History) I have ex- 

 amined a noddy of this group taken on June 13, 1925, by naturalists 

 on the St. George Expedition at a point approximately 350 kilometers 

 west of Isla de Malpelo. 



Family RYNCHOPIDAE : Skimmers ; Rayadores 



The members of this family in general form of wings and body 

 resemble large terns, but in detail differ widely. The bill, compressed 

 laterally from base to tip to a knifelike form, has the lower mandible 

 considerably longer than the upper. This curious development allows 

 a peculiar habit of feeding in which the birds fly low with the breast 

 barely above the water, the head slightly lowered, and the mouth 

 opened wide so that the lower mandible cuts below the surface to 

 pick up small fish and crustaceans. It is this habit that gives them 

 the Spanish name of rayador, varied sometimes to arador, or plow- 

 man, as they seem to draw lines over the surface. Another peculiarity 

 is found in the eye, in which the pupillar opening, when contracted, 

 forms a vertical slit, like that in the eye of a cat (see Wetmore, Proc. 

 Biol. Soc. Washington, 1919, p. 195.) Three species are known, one 

 in the Americas, another in tropical Africa, and the third in south- 

 eastern Asia. 



