The South American Skua 
mussel-shell, and to sever as by a knife the strong abductor muscles, which 
hold the valves together. Its feet, also, are large and strong, and the 
toes are provided with an elaborate set of pectinations which enable the 
bird to maintain a footing upon the most slippery rocks. If the foothold 
on a sloping rock is anywise precarious, the bird retreats backward and 
uphill by means of these convenient calks. 
There is no migratory movement, so far as we are aware, among our 
California breeding birds. There may be some accession to their num¬ 
bers in winter because of a partial retreat of Alaskan birds, but how ex¬ 
tensive this movement may be we have no means of ascertaining. The 
birds are no longer found upon the Farallons, or, more strictly, the 
Southeast Farallon, and there is a noticeable scarcity of them on the 
islands of Humboldt and Del Norte counties, due, no doubt, to human 
persecution rather than to any lack of local attractions. 
No. 266 
South American Skua 
Catharacta chilensis (Saunders). 
Synonyms.— Chilean Skua. Southern Skua. Sea-hawk. 
Description of Catharacta skua Briinnich.— Adult: “Head and nape umber- 
brown; neck rather paler, the acuminate feathers streaked with yellowish brown, 
ruddier at the junction with the back, which is more or less streaked with rufous; wing- 
surface darker brown; primaries chiefly umber, the exposed basal portion of the inner 
webs white, forming a band which is very conspicuous when the bird is flying; quill- 
shafts chiefly white; tail-coverts brown streaked with dull rufous; rectrices umber; 
under surface up to the throat pale chestnut brown; under wing-coverts dark brown 
with a little rufous at times; bill black, the cere with a grayish tinge; iris dark brown; 
tarsi and toes black” (H. Saunders). A melanotic phase also occurs in which the back, 
wings, and exposed portions of tail are sooty black, and the remaining plumage nearly 
uniform sooty brown; the white patch on primaries, as before. Immature birds are 
very much like adults, but they are noticeably smaller; the sharpening as well as stria- 
tion of the neck-feathers is less pronounced; and their coloration in general is duller and 
more blended. Length 508-558.8 (20.00-22.00); wing 393.7-406.4 (15.00-16.00); tail 
152.4 (6.00); bill 57.2 (2.25); tarsus 68.6 (2.70). 
Description of C. chilensis. — Adult: “Similar to the preceding species [ C. skua] 
but much brighter in coloration. Forehead, crown, and occiput dark brown, hind neck 
brown with narrow whitish streaks, and mottled with chestnut; feathers of the mantle 
brown with bright chestnut central streaks; upper tail-coverts chiefly chestnut, with 
brown mottlings; rectrices dark brown; wings dark brown with white visible at the 
bases of the four outer pairs of quills, and more conspicuous on the under side; chin, 
throat, under neck, breast and abdomen warm chestnut; under wings, axillaries, and 
under tail-coverts chiefly chestnut, mottled with brown; bill reddish black; tarsi black 
often mottled with yellowish; toes black. Total length 21 inches [533 mm]; culmen 2.3 
[58.4]; wing 15.5 [393.7]; tail 6.5 [165.1]; tarsus 2.75 [69.85]; middle toe with claw 
2.8 [71.1 ]” (Saunders). 
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