838 
U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
STERCORARIUS, Brisson. 
Stercorarius, Briss. Omithologie, 1760.' 
Cii. —Bill rather strong; the culmen straight and covered at the base with a smooth cere, the end curved. Nostrils linear 
and more open anteriorly. Wings pointed ; first quill longest. Tail of moderate length ; the two middle feathers elongated. 
Tarsi strong, and covered with prominent scales; claws sharp and much curved. Feet fully webbed; hind toe short and 
but little elevated. 
Of this genus there are four species inhabiting North America equally with Europe, as 
follows : 
Very compact in form ; color entirely dark ; bill very strong ; central tail feathers projecting 
but little beyond the others, and not at all pointed.... S. catarractes. 
Upper plumage dark ; light underneath ; central tail feathers exceeding the others about 
two inches, and of a uniform width to the end... S. pomarinus. 
Upper plumage dark ; under light; central tail feathers extending about three inches beyond 
the others, not varying much in width until near the end, when they rapidly become narrower 
to the point. S. parasiticus. 
Dark colored above ; under plumage light ; middle tail feathers projecting about eight inches 
beyond the others, and gradually tapering to a fine point. S. cepphus. 
STERCORARIUS CATARRACTES, T e m m . 
The Common Skua. 
Larus catarractes, Linn. Syst. Nat. I, 1766, 226. 
Stercorarius catarractes, Temm. Man. d’Orn. II, 1820, 792.— Lawr. Am. Lyc. N. Y. VI, 1853, 7.— Bon. Consp. II, 
1856, 206. 
Lestris catarractes, Bonap. Synop. 1826, No. 304.— Nutt. Man. II, 1834, 312. 
Catarracta skua, Brunn. Orn. Bor. 
Sp. Ch.—T he plumage of the upper surface is dark brown, having the feathers tipped with gray ; wings chocolate brown, 
with their shafts and basal parts white ; tail dark brown, white at the base ; under plumage dark grayish brown ; bill black, 
with a tinge of dull blue ; legs and feet black. The central tail feathers extend one inch beyond the others. Length, 22 inches ; 
wing, 15 inches ; bill, 2| ; tarsus, 2| ; tail, 5|. 
Ilab. —Coast of California. 
This species has been rarely obtained in the United States. It may easily be distinguished 
from all others of the genus by its very robust form, the dark color of the adult, and the 
conspicuous white mark on the wing. There is a specimen in my possession obtained off the 
coast of California. 
STERCORARIUS POMARINUS, Tern mi nek. 
The Pomarine Skua. 
Lestris pomarinus, Temm. Man. d’Orn. II, 1815, 514. —Bonap Synop. 1826, No. 305.— Rich. & Sw. F. B. A. II, 
1831 429.— Nutt. Man. II, 1834, 315.— Aud. Birds Amer. VII, 1844, 186 ; pi. ccccli.— Bon. 
Consp. II, 1856, 207. 
Stercorarius pomarinus, Temm. Man. d’Orn. II, 1820, 793. 
