196 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



dark gray, tail coverts in some plain white ; rectrices white, becoming 

 gray on the outer webs of the outer feathers, with black subterminal 

 band, and a white tip; sides of throat and breast gray ; rest of under 

 surface white, barred more or less on sides with gray to brownish 

 gray; under wing coverts white, barred narrowly with gray to 

 brownish gray. 



There is also a dark phase in which the under parts are gray to 

 slate color, edged with white. 



Immature, above black to fuscous-black; hindneck with concealed 

 white and buffy edgings on back ; below streaked more or less with 

 buffy white; upper tail coverts buffy white, barred irregularly with 

 cinnamon brown; under wing coverts barred with black and buffy 

 white ; tail light gray, edged with dull black, and with many narrow 

 bars of fuscous. 



Measurements (from Friedmann, U. S. Nat. Mus. Bull. 50, pt. 10, 

 1950, p. 234).— Males, wing 404-430 (416.4), tail 194-207 (200.6), 

 culmen from cere 23.5-27.5 (25.0), tarsus 92.0-95.0 (93.7) mm. 



Females, wing 423-450 (438.8), tail 198.5-211 (201.4), culmen 

 from cere 25.5-28.5 (27.5), tarsus 84.5-93.0 (87.1) mm. 



Resident. Rare; recorded from Calovevora and Chitra, Veraguas 

 (Salvin, Proc. Zool. Soc. London, 1870, p. 215) ; Cricamola, 

 Bocas del Toro (female in University of Cincinnati Museum, taken 

 by von Wedel October 15, 1936). There are sight records from the 

 western Province of Panama; at El Espino (near the boundary of 

 Code) and Cerro Campana; also at Paris, Herrera; and on Isla 

 Taboga. 



On March 4, 1948, I recorded one soaring near the Rio Santa 

 Maria, northeast of Paris, Herrera. In March 1951 I saw a pair on 

 several occasions soaring in strong wind across the southern slopes of 

 Cerro Campana. They often hung poised for several minutes over 

 one spot, usually with partly closed wings. Once as one remained 

 in that fashion I could see a small bird held in one foot. Occasionally 

 one of these birds came down to perch on a rock at the crest of a 

 ridge, but they were wary and never allowed close approach. On 

 March 24, 1951, I recorded a pair that flew up from perches on rocks 

 on a high ridge above the Rio Calabozo at El Espino. 



On Christmas day, 1955, on Isla Taboga a great ascending thermal 

 that formed over the hill slopes early in the forenoon drew scores of 

 brown pelicans, frigatebirds and vultures that came from afar to 

 soar over the island. Among them I saw a white-tailed hawk that 

 presently drifted away toward Cerro Cabra on the opposite mainland. 



