Parasitic Jaeger 13 
b! Tail distinctly forked. Xema, p. 21. 
b. Bill long, straight and rather slender; both mandibles equal. 
a' Tail short and nearly square; webs between the toes 
emarginate, Hydrochelidon, p. 24. 
b! Tail very distinctly forked; outer feathers elongated and 
pointed ; toes fully webbed. Sterna, p. 22. 
Family STERCORARIID. 
Characters of the only genus. 
Genus STERCORARIUS, 
Bill stout and gull-like with a terminal hook covering the tip of 
the lower mandible, the basal two-thirds covered by a horny cere 
which overlaps the nostrils, so that the opening is much reduced ; 
wings long and strong, outer primary the longest ; tail with the two 
centre feathers much produced; anterior toes fully webbed, hallux 
small and stumpy. 
Three species on the coasts of the United States. 
Parasitic Jaeger. Stercorarius parasiticus. 
A.O.U. Checklist no 37—Colorado Records—Ridgway 79, p. 232; 
Drew 85, p. 18 ; Morrison 89, p. 147; H. G. Smith 96, p. 48 ; Cooke 97, 
p. 50; Henderson 03, pp. 234, 109 ; 09, p. 225. 
Description.—Adult—In the sooty form or dark phase the plumage 
is dark brown throughout, darkest on the mantle, wings and tail; 
neck with acuminate rigid feathers streaked with golden straw ; outer 
primaries with white shafts. The light phase has the upper-parts 
slaty, becoming blackish on the crown, wings and tail, the throat and 
under-parts white; bill brownish-horn, darkest in front of the cere; 
legs black. Length about 18-0; wing 12-0; tail 4:5; to end of central 
feathers 8:0; culmen 1°3; tarsus 1-85. 
Distribution.—The Parasitic Jaeger has a circumpolar range in both 
hemispheres, breeding in America in Alaska, the Barren Grounds and 
Greenland, and wandering in the winter to South Africa, New Zealand 
and portions of South America, chiefly along the coast. It is only 
occasionally found inland. 
This bird is a rare fall and winter straggler in Colorado. There 
was an example in Mrs. Maxwell’s Museum, taken near Boulder, in 
December, sometime before 1874; H. G. Smith examined a young 
male in the dark phase, shot on Sloans Lake near Denver in the fall 
of 1889, and Lowe obtained « third example, now in his collection, 
on the Arkansas River below Pueblo in the fall of 1894, 
