334 Field Museum of Natural History — Zoology, Vol. IX. 



Distr.: Northern hemisphere, breeding chiefly (in North America) 

 from North Dakota to Alaska and casually to the Gulf of St. Lawrence. 

 The greater number go south in winter to the Gulf states, Mexico, and 

 the West Indies. 



Adult male: Head and neck and upper breast, black, showing green- 

 ish reflections; back, grayish white, delicately lined with fine, wavy 

 lines of black, giving it a grayish appearance; 

 speciiliDii, zvhite; under parts, white, the lower 

 belly showing grayish tinge. Length, 19; wing^ 

 8.50; tarsus, 1.50, bill, 2. 



Adult female: Patch at 

 the base of the bill, white or 

 grayish white; rest of the 

 liead and neck, breast, and 

 upper back, brownish; belly, 

 white; speculum, white. 



Length, 17.75; wing, 8.25; 

 tarsus, 1.30; bill, 1.60'. 

 The Scaup Duck occurs on Lake Michigan and waters in the in- 

 terior of Illinois and Wisconsin during the migrations. More or less 

 common, varying in different seasons, but rare in comparison with 

 next species. 



54. Marila affinis (Eyton). 

 Lesser Scaup Duck. 



Aythya affinis (Eyt.), A. O. U. Check List, 1895, p. 53. 

 Local name: Bluebill. 



Distr.: North America in general, breeding chiefly north of the 

 United States; south in winter to the Gulf coast and West Indies, 

 Mexico, and Central America to Panama. 



Adult male: Resembles the male of the preceding species, but is 

 somewhat smaller in size; the head generally shows a faint gloss 

 of purplish, which in the Scaup Duck is usually 

 greenish, and the wavy black bars on the flanks- 

 are more distinct and heavier; speculum, ivhite. 



Length, about 17; wing, about 8.10; tarsus- 

 1.50; bill, 1.75. 



Adult female: Similar to the female of the pre- 

 ceding species, except that it is smaller. 



The white speculum (band on the wing) will 

 always distinguish this species in any plumage from 

 the Ring-necked Duck, which has the speculum gray. 

 Length, about 16.25; wing, about 7.75; bill, about 1.55. 



