540 



DIVING BIRDS. 



a small first toe, and the absence of bare tracts on the sides of the neck ; while the 

 metatarsus is compressed and knife-like. In the clivers the three front toes are 

 fully webbed, and furnished with sharp claw-like nails ; the number of primary 

 quills in the wings is eleven ; the tail, although short, is normal ; and there are 

 but fourteen or fifteen vertebrae in the neck. Moreover, the beak is long, sharp, 

 and compressed ; while . the lores are completely feathered. Apart from the 

 question of their relationship to the auks, the peculiar structure of the tibia 

 seems clearly to indicate an intimate affinity between the divers and the grebes. 

 Although an extinct representative of the family (Colymboides) has left its 

 remains in the Miocene deposits of the Continent, the existing divers, of which 

 there are three well-marked species confined to the Arctic and cooler regions of the 

 Northern Hemisphere, are included in the single genus Colymbus. The divers, al- 

 though more slenderly 

 formed, have some- 

 what the appearance of 

 geese when seen on the 

 water; but on land, 

 owing to the backward 

 situation of their legs, 

 are widely different. 

 In plumage, the two 

 sexes are alike; but 

 the winter dress differs 

 considerably from that 

 of summer, as do the 

 young from the adult. 

 The typical representa- 

 tive of the genus is the 

 great northern diver 

 (C. glacialis), attaining 

 a length of some 33 

 inches, and character- 

 ised by its glossy black head and neck, the presence of two gorgets of velvety black 

 and white stripes on the throat, and the belts of white spots of varying size crossing 

 the dark back; the under-parts being white. Not uncommon especially in an 

 immature state on the British coasts, and thence wandering as far south as the 

 Mediterranean, this diver breeds in Iceland, Greenland, and North-Eastern Canada ; 

 while in North-Eastern Asia and Western Arctic America it is replaced by a larger 

 variety (C. adamsi), distinguished by the white or yellow hue of its beak. Next 

 in point of size is the black-throated diver (C. arcticus), which does not exceed 26 

 inches in length, and is characterised by its light grey head, the purplish black 

 patch, surmounted with a black-and-white striped gorget on the throat, and the 

 presence of two elongated areas on the black back between the shoulders, as well 

 as others on the scapulars, marked by transverse white bands formed by nearly 

 confluent square spots. The breeding-area of this species would seem to extend 

 from the Hebrides and Scandinavia across Arctic Asia over the greater part of 



GREAT NORTHERN DIVER. 



