BIRDS OF NORTH AND MIDDLE AMERICA 681 



FALCO ALBIGULARIS PETROPHILUS van Rossem and Hachisuka 



SoNORA White-tiiroated Falcon 



Adult. — Similar to the nominate form but differs in the color of 

 the upperparts, which are plumbeous-slate instead of plumbeous- 

 black or blackish plumbeous, this difference being particularly 

 noticeable on the pileum, forehead, and cheeks; throat, upper breast, 

 and partial collar around hindneck white, averaging more faintly 

 tinged with buffy where adjoining dark portions, as opposed to deeper 

 buff to ochraceous; reddish brown of median underparts and thighs 

 slightly paler. ^^ 



Other plumages. — Not seen. 



Adult male. — Wing 192, 192; tail 90.5, 99; culmen from cere 11.5, 

 12.5; tarsus 33.5, 33; middle toe without claw 30.5, 30.5 mm. (2 

 specimens from Guirocoba, including the type). 



Adult female. — Wing 224, 228; tail 118, 118; culmen from cere 14.5, 

 15; tarsus 36, 38; middle toe without claw 34, 36 mm. (2 specimens from 

 Mazatlan and Guirocoba). 



Range. — Resident in the foothills of the arid Tropical Zone from 

 extreme southeastern Sonora (Guirocoba) to Sinaloa (Sierra Madre 

 (?), Plomosas, and Mazatldn), east to southwestern Tamaulipas 

 (Gomez Farias), where it intergrades with the nominate race. 



Type locality. — Guirocoba, southeastern Sonora. 



Falco rufigularis Salvin and Godman, Biol. Centr. Amer., Aves, iii, 1901, 116, 

 part (Sierra Madre (?) and Mazatldn, Sinaloa). 



Hypotriorchis rufigularis Lawrence, Mem. Boston Soc. Nat. Hist., ii, 1874, 301, 

 part (Mazatldn, Sinaloa). 



Falco albigularis petrophilus van Rossem and Hachisuka, Proc. Biol. Soc. Wash- 

 ington, 1, 1937, 107 (Guirocoba, Sonora; descr.); Auk, Iv, 1938, 309, in text 

 (Sonora; breeding). — Sutton and Burleigh, Occ. Pap. Mus. Zool. Louisiana 

 State Univ., No. 3, 1939, 27.— Sutton and Pettingill, Auk, lix, 1942, 10, 

 in text (G6mez Farias region, sw. Tamaulipas, intermediate). — van Rossem, 

 Occ. Pap. Mus. Zool. Louisiana State Univ., No. 21, 1945, 63 (Sonora). 



Subgenus Rhynchofalco Ridgway 



Medium-sized, rather slender falcons (wing about 233-295 mm.) 

 with tail much longer than distance from tip of longest primary to 

 tip of longest primary covert; length of cere on top equal to more than 

 one-third the length (curve) of culmen; depth of bill at base at rham- 

 photheca equal to distance from anterior edge of cere (in front of 

 nostril) to tip of maxilla; distance from bend of wmg to tip of longest 

 primary covert decidedly less than from latter point to tip of longest 



52 In the original description van Rossem and Hachisuka write that a specimen 

 "from Mazatldn, Sinaloa . . . seems to approximate the characters of petro- 

 philus." I have seen this Mazatldn specimen and it is paler above than any of 

 a good series of the nominate race, and I therefore place it with this race. 



