IV FALCONIDAE 1 47 



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, lied- 

 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, Loplioaetus,^Thrasaetus, 

 Hnrpyhalicoetus, Helotarsvs, Morphnus, and Zojjhoictinia being 

 especially noticeable ; Circus has a facial ruff, coupled with excep- 

 tionally large aural apertures ; the feathers of the neck may bo 

 lanceolate, as in Haliaetus, or those of the nape, as in Aquila ; 

 and the plumage commonly over-hangs the metatarsus, wdiich is 

 feathered to the toes in various Aquiline forms, and in Archihuteo. 

 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-families : 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 ; Gypaetus, 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 

 Kitzsch ^ has recorded single or paired powder-down patches on 

 the lower back of Elano'idcs, Ulmms, Eegerhinus, and Circus, with 

 similar but scattered down-feathers in Gypaetus. 



The members of this Family range in size from the mighty 

 Lammergeier to the tiny Finch-Falcon (Microhierax) ; but they 

 have many habits in common, though Polylorus and Milvago 

 are somewhat terrestrial and vulturine, and a few species have 

 crepuscular tendencies. They are decidedly non- gregarious, 

 though the Polyborinae, Erythropus, 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 v/oods, they can bear the 

 cold of the icy regions or the heat of the Equator, but towards 

 ^ J'icrylograjJhy {Hay Soc.) ed. Sclater, 1867, p. 37. 



