176 DIURNAL BIRDS OF PREY. 



oil-gland is crowned with a circle of feathers. Inferiorly the windpipe is provided 



with an organ of voice. Although very closely connected by the lammergeier, 



the falcons and their allies differ from the vultures (except the lammergeier) by 



the head being clothed with true feathers, and bj' the size of the females exceeding 



that of the males. The group includes the smallest members of the order, while 



its largest representatives are second only in size to the vultures. As a rule, these 



birds subsist mainly or exclusively on prey killed by themselves, although some 



will eat carrion, and a few feed on honeycomb. Like other Accipitrines, the two 



sexes associate in pairs, which mate for life ; while the number of young produced 



in a brood seldom exceeds four, and is frequently less. They have a cosmopolitan 



distribution, and may be divided into five subfamilies. 



The true falcons, as represented by the peregrine and the 

 True Falcons. . jt o 



kestrel, are the typical members of a subfamily, characterised by 



the length of the tibia being considerably greater than that of the metatarsus, 

 by the scutes on the hinder aspect of the metatarsus being arranged in a reti- 

 culate manner, and by the sides of the bill being notched. In all of them the cere 

 is large, and often brightly coloured. With regard to the extent of the genus 

 Falco, there is a certain amount of difference of opinion among ornithologists, 

 some, including in it the whole of the European falcons, while others separate the 

 gerfalcons (as Hierofalco), and the kestrels (as Tirinumcultus, or Cerchneis). Used 

 in the wider sense, the genus will include (with the exception of one peculiar species 

 from the Argentine and another from New Zealand) all the falcons in which the 

 nostrils are circular and furnished with a distinct tubercle in the middle. The 

 beak in all is short and curved, with one notch in the upper mandible ; the wings 

 are long and pointed, with the first and third quills of equal length, and the second 

 the longest ; and the toes are elongated. Many of the larger species have a distinct 

 dark stripe on the cheek, which in the peregrine expands into a large patch. All 

 are subject to great variation of plumage, according to age, which renders the 

 discrimination of many of the species a matter of exceeding difficulty. 



Under the common title of gerfalcons are included several closely 



Qerfalcons. . . "^ 



allied falcons of large size, from the northern regions of the Northern 



Hemisphere, distinguished by the comparative shortness of the toes, more especially 

 the fourth, which (exclusive of the claw) is about equal in length to the second. 

 The wings, moreover, are rather short, and the length of the interval between the 

 tips of the primary and secondary quills does not exceed half the length of the tail. 

 The beak is somewhat elongated ; and the colour of the plumage tends to slaty 

 grey, or white; these being the only falcons in which there is such a type of 

 coloration. One of the best known of these species is the Greenland falcon 

 (Falco candicans), of Greenland and 'North America, young birds occasionally 

 straggling to the British Islands. This is the lightest - coloured member of the 

 group, and is hence sometimes termed the white gerfalcon. Its distinctive 

 characters are to be found in the yellow tint of the cere, beak, and claws ; and 

 by the ground-colour of the plumage being white at all ages. In old birds, the 

 head, under-parts, and tail become almost, or completely, white ; while the upper- 

 parts retain small black spots. In the young the breast and flanks are longi- 

 tudinally streaked with brown. The length of the female reaches 23 inches. In 



