78 BULLETIN 15 3, UNITED STATES NATIONAL MUSIiUM 



gion are bare. The incoming pennaceous feathers of the juvenal 

 plumage on the upper parts are darker, more fuscous black then the 

 corresponding feathers in older, but still immature (or at least sub- 

 adult), birds and have no rufous terminal margins. This last fact, 

 particularly, indicates that the species takes at least three years to 

 acquire adult plumage, the four plumages being as follows : 



1. Natal Down. — ^White. 



2. Juvenal fluniage. — Above dark fuscous or fuscous black, the 

 rectrices dark gray barred with black; below white, the breast and 

 abdomen (and probably the thighs as well) heavily spotted with 

 rich rufous. 



3. Immature plumage. — Similar to the juvenal stage but lighter 

 above and all the feathers of the back, head, and wing coverts nar- 

 rowly margined with rufous, which edgings gradually wear off. 

 Birds in this plumage vary considerably in the intensity and size of 

 the brown ventral spots. The flanks and sides are barred, not spotted. 

 In some individuals the throat is pure white, unmarked with darker 

 color, but in others it is streaked with dusky brownish gray. 



4. Adult ylwnage. — This plumage is well known and needs no rede- 

 scription here. 



Three African forms of this hawk have been named — sphenurus^ 

 riggenbachi., and polyzonoides. The first and the last are the ones 

 usually recognized, while riggenhachi is more or less in dispute. 

 Hartert, Van Someren ^- and Sclater " conclude that it is merely a 

 dark phase of sphenurus., and the facts seem to indicate the sound- 

 ness of their decision, as riggenbachi has been taken only in places 

 where sphenurus is known to occur. It is extremely unlikely that 

 the former is a distinct species, and yet so like sphenm^s and geo- 

 graphically and ecologically coincident with it. 



The southern form polyzonoides is unusually well marked, and has 

 been considered as a distinct species by Swann.^* Sclater, Strese- 

 mann, and others consider it a race of hadius. The material available 

 to me leads me to regard it as a race of hadius and not as a species 

 by itself. Although the adults of the two races are quite distinct, 

 the distinction is due merel}?^ to lack of intergrading specimens. The 

 immature plumages of the two are similar but the brown markings 

 on the undersides are lighter, more cinnamomeus in polyzonoides 

 than in sphenurus. 



The ranges of the two races are more extensive than usually 

 thought. Swann ""^ gives that of polyzonoides as South Africa north 

 to Nyasaland, while Sclater "^ adds Northern Khodesia and Tangan- 



" Nov. Zool., vol. 29, 1922, p. 40. 



" Syst. Avium, 1924, p. 69. 



'* Monogr. Birds of Prey, pt. 4, 1925, p. 220. 



■^Sj-nopsls of Accipitres, 1922, p. 41. 



™ Syst. Avium Ethiop., 1924, p. 70. 



