AVES FALCONID^. 573 



Neck: Above and on the sides concolorwith the crown and occiput and 

 with an undertone of deep rich brown. Chin, throat and lower neck pure 

 white, abruptly defined against the black areas and head and neck. 



Back : Upper and lower back shining black, with an undertone of deep, 

 rich brown ; rump and upper tail pure white. In some adults this is more 

 or less spotted with chocolate, but in most cases the rump-patch is 

 immaculate. 



Tail : White at base, where the shafts of the rectrices are ivory-white ; 

 then a black region six inches or more in extent toward the terminal pure 

 white band an inch and a half broad, the rectrices here having white shafts ; 

 the feathers of the tail are generally so worn terminally (even in newly- 

 moulted birds), by the terrestrial feeding habits of the species as to make 

 this terminal white band appear much narrower. The tail from below 

 presents much the same pattern, but is duller, so far as the black region is 

 concerned. 



Wings: Black, with the prevailing undertone of deep, rich brown. Pri- 

 maries white at the base, the outer vanes wholly black with brown shade ; 

 the inner vanes barred black and white for the basal third, then wholly 

 black or brown tone, till at the end they are tipped definitely with white on 

 the first three quills, the others having very obscure edging of white at 

 tips. Secondaries barred on their inner vanes black and white basally, 

 then black, with deep brown undertone, and all broadly tipped with pure 

 white. Rest of the upper surface of the wing black like the back; the 

 white feathers at the bend of the wing in the ulnar-radial region extend 

 slightly on the upper surface, so as to be conspicuous when the wing is 

 closed. 



Lower parts : Immaculate pure white throughout, including the under 

 wing-coverts and axillaries ; most adult birds have a few black or dark 

 feathers showing as bars on the thighs, but this marking is not always 

 present. 



Bill: "base of bill yellow" (J. B. Hatcher). The bill is yellow, with 

 blue shadings near the cere. Cere "yellow" (Charles Darwin). 



Feet: "Yellow" (Charles Darwin, from type). 



Iris: Hazel. Hazel-brown (J. B. Hatcher). 



"Une femelle de cette espece a ete tuee par M. Lebrun le i6 juin 1883 

 sur les bords du Rio Gallegos. Elle avait les yeux d'un jaune fonc6 et 

 la cire d'un jaune orange. Au contraire, le type de \ Ibycter albigularis 



