160 LIFE HISTORIES OF NORTH AMERICAN DIVING BIRDS 



Juvenal plumage is acquired in August; this is sooty black above and 

 white below heavily mottled with dusky on the sides, less heavily 

 on the belly and breast, and only very finely spotted on the throat 

 and chin. The white wing patches are much concealed by the broad 

 dusky tips of the feathers. The Juvenal plumage is soon replaced 

 by the first winter plumage, which is similar to the adult winter 

 plumage but with less white and more dusky; there is much more 

 dusky on the head, and the white wing patches are broken by black- 

 tipped feathers; this plumage is worn all winter, but is molted wholly 

 or partly into the black plumage during the first spring. I believe 

 that young birds molt later in the spring than adults and that the 

 molt is often less complete than in adults, producing a variety of 

 mottled black and white plumages. The change into the adult winter 

 begins in August but is not completed until October or later; winter 

 adults may be distinguished from young birds by the greater propor- 

 tion of white, particularly on the head, and by the pure white wing 

 patches. The spring molt, which includes all but the wings and tail, 

 is considerably prolonged or varies greatly in date with different 

 individuals. Some birds acquire their full summer plumage as early 

 as the 1st of February, but I have seen birds during the first week in 

 May in practically full winter plumage, and have birds in my col- 

 lection in various stages of molt taken as late as June 18. 



Food. On the coast of Maine the black guillemot feeds largely 

 on rock eels (Gunnellus gunnellus), small fish which can be found at 

 low tide under loose stones. It also eats small mussels and other 

 small mollusks, which it obtains by diving and swallows whole, sea 

 insects, marine worms, shrimps, small crabs, and other small crus- 

 taceans, which swim on or near the surface. Small fish are fre- 

 quently included in its diet. Mr. Lucien M. Turner, in his unpub- 

 lished notes on the birds of Ungava, says: 



The food of the birds is essentially marine, consisting of all manner of 

 smaller Crustacea. Several stomachs were opened and found to contain re- 

 cently swallowed specimens of Mysis mixta only; no other food being apparent. 

 Other stomachs contained only a semiviscid fluid of reddish amber color, such 

 as might result from the digestion of such food as that just mentioned. 



Behavior. The only note that I have heard this species utter is a 

 faint, shrill, piping whistle which is apparently used as a call rather 

 than an alarm note. When disturbed on its nest it emits a hissing 

 note of protest. It is usually silent, however. 



Its flight is strong, swift, and direct, with rapid wing strokes, 

 usually close to the water. In diving it flops under the surface with 

 open wings, using them regularly in subaqueous flight. Dr. Charles 

 W. Townsend writes to me: 



The habit possessed by the black guillemot of dabbling with its bill at the 

 water may have arisen in attempts to obtain food or to sip the water, but it 



