THE WHITE-BILLED NORTHERN DIVER. 469 



colour varying from olive to deep umber-brown, and generally 

 some black blotches but not always. Average size of 100 eggs, 

 89.8x57.6. Max.: 101.5x62.5. Min. : 85x54.5 and 86.1 X 54.3 

 mm. Breeding -season. — From early June onward in Iceland. 

 Incubation. — By both sexes. Period 30 days. Single brooded. 



Food. — Chiefly fish, including flounders, sand-launce (Ammodytes). 

 father-lasher (Cottus), gurnard, pipe-fish, herring, etc. Also 

 Crustacea (crabs (Portunus, Carcinus, etc.), shrimps, prawns, etc.) ; 

 mollusca (Solen) ; cephalopoda, and vegetable remains. 



Distribution. — British Isles. — Winter-visitor (mid-Sept, to May). 

 Fairly generally distributed all coasts, but most plentiful in north. 

 In 0. Hebrides and Shetlands present most times of year, and has 

 been thought several times, but never proved, to have bred in 

 latter. Not uncommon inland waters. 



Distribution. — Abroad. — Breeding Iceland, Greenland and eastern 

 N. America ; apparently Jan Mayen. Wintering North Sea, south 

 to western Mediterranean and even rarely Madeira and Azores, 

 once or twice Baltic Sea, casually inland waters Europe as far as 

 Bohemia and Transylvania, Black Sea ; in America known to 

 North Carolina. According to Bishop replaced by smaller race in 

 interior of N. America from N. California north at least to British 

 Columbia, wintering chiefly on coast of California south to Lower 

 California and Florida. 



COLYMBUS ADAMSII 



357. Colymbus adamsii Gray — THE WHITE-BILLED 

 NORTHERN DIVER. 



Colymbus adamsii Gray, Proc. Zool. Soc. London, 1859, p. 167 (Alaska). 

 Colymbus adamsi Gray, Yarrell, in, p. x ; Saunders, p. 711. 



Description. — Adult male and female. Winter. — Like O. immer 

 but shafts of primaries (except at tips) pale brown to brownish- 

 white instead of dark brown.* Very few moulting examples avail- 

 able but appears to moult as in G. immer. Summer. — Complete 

 moult as in C. immer. Like C. immer but whole head, neck and 

 throat glossed purple rather than green, white streaks on throat 

 and neck broader but fewer in number, white spots on upper-parts 

 larger, this being especially noticeable on scapulars, shafts of 

 primaries as in winter pale brown. 



Nestling. — (Not examined.) 



Juvenile. — As in C. immer but shafts of primaries (except at 

 tips) pale brown, lesser wing-coverts rather more streaked with 

 grey than in C. immer. 



Measurements and structure. — £ wing 375-395 mm., tail 56-67, 

 tarsus 89-96, bill from nostril 60-76 (4 measured). ? wing 360-385, 



* One example (Brit. Mus.) has dark brown shafts, so that this char- 

 acter appears not to be invariable. — H.F.W. 



