304 Birds of Colorado 
feet from the entrance, which was barely large enough 
for the Wren to squeeze through much less the Cow-bird. 
Aiken informs me he once found in Wet Mountain 
Valley a Yellow Warbler’s nest, built in three stories, 
the lower one of which contained eggs of the Cow-bird ; 
it is presumed that the successive stories were built 
by the Warblers to avoid hatching the Cow-bird eggs. 
The eggs of the Cow-bird are very strongly shelled ; 
whitish in colour, profusely speckled with reddish- 
brown ; they average 84 x °65 in measurement. 
Genus XANTHOCEPHALUS. 
Medium-sized birds—wing under 6—with a stout, conical bill, shorter 
than the head, the culmen straight, not decurved ; nostril oval, over- 
hung by & prominent operculum; wings long and pointed ; the outer 
(ninth) primary usually the longest ; tarsus stout, nearly twice es long 
as the culmen ; plumage black or dusky, and yellow. 
The Yellow-headed Blackbird is the only species assigned to this genus. 
Yellow-headed Blackbird. Xanthocephalus xanthocephalus. 
A.O.U. Checklist no 497—Colorado Records—Baird 58, p. 531 
(X. wcterocephalus); Aiken 72, p. 202; Henshaw 75, p. 315; Scott 
79, p. 94; Minot 80, p. 230; Allen & Brewster 83, p. 193; Drew 
85, p. 16; Beckham 85, p. 142; Thorne 88, p. 112; Morrison 89, 
p. 148; Lowe 92, p. 101; Cooke 97, pp. 18, 93, 211 ; Keyser 02, p. 141 ; 
Dille 03, p. 74; Henderson 03, p. 236; 09, p. 234; Warren 06, p. 22; 
08, p. 22; 09, p. 15; Markman 07, p. 157; Gilman 07, p. 156; 
Rockwell 08, p. 169; Hersey & Rockwell 09, p. 118. 
Description.—Male in summer—Head, neck and chest bright orange- 
yellow; a patch round the eye and base of the bill and the whole of 
the rest of the plumage black ; a white patch on the base of the wing 
involving the primary and some of the greater coverts; a rather 
indistinct yellow anal-patch ; iris brown, bill and legs black. Length 
10-5; wing 5-75; tail 4-65; culmen -85; tarsus 1-50. 
In winter the yellow of the crown and hind-neck is obscured by dusky 
tips to the feathers. The female is much smaller than the male (wing 
about 4-5) ; it is dark sepia-brown in colour with the superciliary stripe, 
chin, throat and upper-breast dull yellow, and the lower-breast streaked 
with white; no white wing-patch. The young male resembles the 
female, but is larger and somewhat darker, both as regards the brown 
and the yellow. 
