THE WHITE-BILLED NORTHERN DIVER. J 7' 



The White-billed Diver is rather larger than the Northern Diver, and has a 

 longer bill, which measures along the culmen from 3^50 to 3^75 inches. The 

 cnlmen is straight, not curved, and the under mandible bent up suddenly to meet 

 it, rather less than half way from the tip. In the adult the bill is yellowish-white, 

 a little dusky at the very base of the lower mandible ; in the young it is whitish, 

 dusky at the base. 



In summer the black of the chin, throat and forepart and sides of the neck 

 is bluish, with a violet gloss, and that of the upper part of the head and the 

 back of the neck greenish. In C. glacialis the gloss on the throat and neck 

 (except the lowest portion) is green. The crown of the head is of much the same 

 colour as that of C. glacialis. The white streaks of the throat collar number about 

 half a dozen instead of a dozen ; those of the patches on the sides of the neck, 

 about ten instead of about twenty in C. glacialis. These patches or bands on the 

 sides of the neck are broadest in the middle, whereas in C. glacialis they are 

 broadest at the back of the neck ; this character is a very striking one. The white 

 spots on the scapulars are large and oblong, whereas in C. glacialis they are smaller 

 and square. The lower part of the back is (in adults) usually quite unspotted. 

 The spots on the rump are fewer than in C. glacialis. Professor Collett 

 points out that the shafts of the wing feathers are light horn brown, except the 

 tips which are brownish-black, while in C. glacialis the whole outer half of the 

 shafts is brownish-black. And he adds that in this character of C. adamsi there 

 is no difference between young and old birds ; it is therefore of especial value, 

 " being the only distinguishing feature present even in the young bird, and its 

 investigation will determine in an instant to which species any individual specimen 

 is to be referred" ("Ibis," 1894, p. 278). 



