62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



Description. — Length 760 to 860 mm. Adult, back (except for 

 center), wings, and tail, grayish brown, the feathers in the center of 

 the back tipped with white ; head and neck gray mottled with white ; 

 under surface, upper back, and base of neck, white; central tail 

 feathers white, bordered by gray. 



Immature, mottled with dark grayish brown on breast and abdo- 

 men. 



An adult female taken at Farallon del Chiru had the iris clear 

 yellow, while in another from Isla Villa, not as old, it was light 

 grayish brown, with an indistinct line of Marguerite yellow around 

 the external margin. In both the bill was light greenish gray, shad- 

 ing posteriorly into the grayish blue of the face, bare throat, ramal 

 area, lores, eyelids, and a narrow line on the forehead back of the 

 bill ; tarsi and feet light bright blue, with the front of the tarsi, and 

 the basal joints of the toes grayer; claw of middle toe horn color, 

 of other toes neutral gray; bare skin surrounding anus light blue 

 like the webs between the toes. 



Measurements (from Murphy, Oceanic Birds S. Amer., 1936, p. 

 830).— Males (7 specimens), wing 387-413 (403), tail 165-218 

 (190) ; exposed culmen 94-106 (99.7), tarsus 47-54 (50.4) mm. 



Females (7 specimens), wing 403-426 (416), tail 165-215 (190), 

 exposed culmen 106.0-109.5 (107.5), tarsus 51-57 (55) mm. 



Resident. Fairly common in the Gulf of Panama. Breeding colonies 

 are recorded at Isla Villa, off the coast of Los Santos ; Farallon del 

 Chiru, off Santa Clara, Code ; on Isla Pachequilla (probably also on 

 Pacheca and Galera) , Archipielago de las Perlas ; and on Isla Bona. 

 A few pairs probably nest on rocky islets off the western side of 

 Isla Taboguilla. 



At Isla Villa on February 28, 1957, a dozen circled off the rocky 

 summit when the birds resting there were alarmed. And at Farallon 

 del Chiru, on the same day, I noted another dozen pairs. With those 

 at this second locality there were a few dark-colored young. Birds 

 seen flying off Riomar, March 15, 1958, are presumed to have come 

 from this same locality. In the Archipielago de las Perlas, Mrs. 

 Sturgis (Birds Panama Canal Zone, 1928, p. 112) records that "we 

 saw them in considerable numbers in the Pearl Islands on Pacheca 

 and Galera on the ledges of the cliffs." This implies breeding but 

 is not definite; it seems to be the basis for the report of Hellmayr 

 and Conover (Cat. Birds Amer., pt. 1, no. 2, 1948, p. 124) of nesting 

 on these two islands. On two days in January 1960 I found 20 

 grouped on a cliff edge on Isla Pachequilla, and saw several isolated 



