30 THE WORLD'S BIRDS. 



ECONOMIC QUALITIES. There is nothing particular to 

 be recorded on this head, as these birds are not 

 numerous enough to be of any great influence. 



CAPTIVITY. Divers have seldom been kept in captivity, 

 and need much the same treatment as grebes, 

 allowing for their larger size. They have not bred. 



DISTRIBUTION AND IMPORTANT SPECIES. Divers are 

 found all round the Northern Hemisphere, this 

 being one of the families characteristic of this 

 region. They breed in fresh water, and are found 

 in winter on the coasts, only migrating south for 

 open water. Only four species are known, all 

 found in both worlds, the Black- and Red-throated 

 (Colymbm arcticus and C. septentrionalis) , the 

 Great Northern (C. glacialis) and the arctic White- 

 billed (C. adamsi). 



DUCKS (Anatidce). 



DIAGNOSIS. Four-toed water-fowl with a straight beak 

 toothed or ridged in both jaws. 



SIZE. From that of a turtle-dove upwards ; the tame 

 swan is the largest. 



FORM. Bill of medium length or short, usually broad, 

 covered with skin instead of horn, except at the tip 

 (which forms the so-called "nail") and furnished 

 at the edges with horny ridges or " teeth " ; corner 

 of mouth not reaching further back than forehead ; 

 feet with the shanks of medium length or short, 

 the three front toes usually fully webbed, hind toe 

 usually small and useless ; wings of medium 

 length, or short. Body heavy, neck long or very 

 long ; tail short as a rule, and composed of numerous 

 feathers. 



PLUMAGE AND COLOURATION. Very sleek, and much 

 varied in colour ; a conspicuous bar on the secondai y 



