400 BRITISH BIRDS. 



Family COLYMBID^, OR DIVERS. 



The Divers are a well-defined but very small family of birds, containing 

 only one genus, which consists of only four or five species. They are probably 

 nearest related to the Auks, though the majority of ornithologists consider 

 them to have still closer affinity with the Grebes. Sclater places the 

 Grebes between the Divers and the Auks, the three families composing 

 the order Pygopodes. Forbes placed the Divers, the Grebes, and the 

 Ducks in a group by themselves. Gadow also associates the Divers with 

 the Ducks, regarding them as forming with the Cormorants and the 

 Penguins three much specialized families descended from the same 

 ancestors as the less modified family of Ducks. In the arrangement of 

 their palatal bones the Divers most nearly resemble the Grebes, the 

 Auks, and the Gulls ; in the arrangement of their feather-tracts the 

 Divers resemble the Auks to some extent, but most closely the Grebes. 

 There is only one small notch on each side of the posterior margin of the 

 sternum in the Divers, and the lateral processes do not extend so far as 

 the central projection. 



The principal external characters of the Divers are their webbed feet, 

 furnished with a well-developed hind toe, their nearly straight elongated 

 sharp-pointed conical bills, moderately long wings, and short tails. The 

 Divers resemble the Grebes and the Cormorants in having the tarsus 

 laterally compressed so as to cut the water like a knife, and they also 

 resemble the latter birds in having the hind toe on the same plane as the 

 others, and the fourth toe the longest. 



Divers are born covered with down, and are able to swim shortly after- 

 wards. The adults moult all their feathers in early autumn, and begin to 

 assume their nuptial plumage before the end of the year ; but the young 

 retain their first plumage until early spring, when they, like their parents, 

 moult their small feathers only into summer plumage, which differs in 

 many conspicuous ways from that of winter. The plumage of both sexes 

 is alike ; but after the spring moult birds of the year are less brilliantly 

 coloured than adults, though it is said that they are found breeding in 

 this plumage. 



The Divers are arctic or semi-arctic birds, confined to the Nearctic and 

 Palsearctie Regions. 



