Iv FALCONIDAE eg 
and it often takes four years or more to attain maturity, the 
markings commonly changing from longitudinal to transverse ; 
but the sexes are usually alike, though the Kestrel, Merlin, Red- 
footed Falcon, and many Harriers are well-known exceptions, the 
last having generally blue-grey males and brown females. The 
occipital feathers are elongated in several of the Polyborinae, 
and a full crest occurs in many genera, Lophoaétus, Thrasaétus, 
Harpyhaliaétus, Helotarsus, Morphnus, and Lophoictinia being 
especially noticeable; Circus has a facial ruff, coupled with excep- 
tionally large aural apertures; the feathers of the neck may be 
lanceolate, as in Haliaétus, or those of the nape, as in Aquila ; 
and the plumage commonly over-hangs the metatarsus, which is 
feathered to the toes in various Aquiline forms, and in Archibuteo. 
The nostrils are circular in the Falconinae, oval or nearly linear 
elsewhere, with a central tubercle in the last-named and the 
Polyborinae, seldom found in the other Sub-familes: they are 
generally in or near the cere, which is almost always fleshy. An 
aftershaft is present; the down in adults is uniform; that of 
the nestling being woolly and varying from white to grey, buff, 
brown, or black. The feet are yellow, red, or brown; the bill is 
ordinarily dark, and the cere yellow; Gypaétus, however, has all these 
parts bluish-grey, with a crimson sclerotic membrane (equivalent 
to the “ white of the eye ”) round the orange iris, the latter being 
yellow or orange in the Accipitrinae, brown in the Falconinae, and 
varying to red elsewhere. The syrinx has two pairs of tracheo- 
bronchial muscles; the tongue is thick and often concave; and 
Nitzsch* bas recorded single or paired powder-down patches on 
the lower back of Elanoides, Elanus, Regerhinus, and Circus, with 
similar but scattered down-feathers in Gypaétus. 
The members of this Family range in size from the mighty 
Limmergeier to the tiny Finch-Falcon (Mierohierax); but they 
have many habits in common, though Polyborus and Milvago 
are somewhat terrestrial and vulturine, and a few species have 
crepuscular tendencies. They are decidedly non-gregarious, 
though the Polyborinae, Lrythropus, and Rostrhamus form partial 
exceptions ; they pair very early in the year, if not for life, the 
larger forms in especial breeding almost before winter is over. Birds 
of the mountains, the plains, and the woods, they can bear the 
cold of the icy regions or the heat of the Equator, but towards 
2 
1 Pterylography (Ray Soc.) ed. Sclater, 1867, p. 37. 
