472 A PRACTICAL HANDBOOK OF BRITISH BIRDS. 



coverts with grey-brown tips. N.B. — Grey tips of feathers of upper- 

 parts and white tips of tail become considerably worn by January. 



First winter and summer. — From Jan. onwards a varying amount 

 of body-moult takes place, new feathers of mantle and scapulars 

 being uniform black as in adult winter but usually considerable 

 number of old juvenile feathers are retained ; tail also moults 

 (usually partially) new feathers having white tips as adult winter ; 

 wing-feathers and wing-coverts are not moulted. This mixture of 

 plumages appears to be retained throughout first summer until 

 bird is rather more than one year old when moult to winter plumage 

 commences and after this is complete bird is apparently indis- 

 tinguishable from adult, but insufficient material is available to 

 make certain of these points. 



Measurements and structure. — $ wing 280-335 mm., tail 50-61, 

 tarsus 72-80, bill from nostril 40-50 (8 measured). $ wing 268- 

 320, bill 33^3. Primaries : 1st very small and hidden, 2nd 

 longest, 3rd 2-8 mm. shorter, 4th 12-22 shorter, 5th 32-46 shorter, 

 6th 52-65 shorter. Other structure as in C. immer. 



Soft parts. — As in C. immer. 



Characters and allied forms. — C. a. pacificus (N. America) is 

 smaller and in summer has paler back of neck and less prominent 

 white streaks on sides of neck ; C. a. suschkini (W. Siberia) is 

 stated to have paler back of neck and rather larger white spots on 

 upper-parts and C. a. viridigularis (E. Siberia) to have green rather 

 than purple throat. Distinguished from C. immer in summer by 

 grey back of neck, adult winter by absence of grey fringes to 

 feathers of upper -parts, juvenile by smaller size. 



Field -characters. — In breeding dress large white spots on wing- 

 coverts and scapulars and unspotted back, wings and tail contrast 

 with uniformly spotted upper-parts of Great Northern, as does 

 grey of crown and hind-neck. In winter -plumage the two are very 

 similar, and, although Black-throated is smaller as a rule, sizes 

 sometimes overlap. Differs from Red-throated in winter by 

 feathers of upper -parts not being tipped with spots of white but 

 margined with pale grey. Wailing cry described as an unearthly 

 agonized howl ; a hoarse alarm -note is like croak of Raven (Collett) ; 

 another note is a yapping " hy, hy, hy " (Kolthoff). 



Breeding-habits. — Prefers deep-water lochs, often in hills. Nest. 

 — Usually flattened spot near margin of island or shore of lake, but 

 nests built of aquatic vegetation recorded from Continent. Eggs. — 

 Normally 2, 1 in second or third layings, but 3 young have been 

 recorded together. Intermediate in size between those of C. immer 

 and C. stellatus, varying from greenish -olive to dark umber with 

 blackish blotches or spots in some cases. Average of 100 eggs, 

 84.5x51.7. Max. : 95x52.5 and 82x56. Min. : 75.7x51.8 and 

 87x45.5 mm. Breeding -season. — Latter half May and early June 

 in Scotland. Incubation. — By both sexes in turn. Period 28 days 

 (Zedlitz). Single brooded. 



