THE BIRDS OF THE PEIBILOF ISLANDS. 393 



pairs on each feather until the youngster is several weeks old. The swelling on the 

 belly downs is seldom as large as on the others. Usually some swelling is noticeable, 

 but often the rachises of the rami continues into the downs with little appreciable 

 increase of size. The figures in PI. XLI and the explanations opposite will explain 

 these changes. The double effect seen in flg. 19 is common on the belly, and may be 

 caused, by two tufts adhering. The radii of the down rachis lie flat against it pointing 

 upward. They evidently adhere until dried and loosened by friction. The first down 

 of these birds differs from the other species of auks in being stronger and shorter. 



From some hundreds of eggs I selected nine as typical of extremes of color and 

 markings. These are shown in the accompanying photograph, PI. XXXIX. The 

 greater number of eggs, by far, is made up of intermediates. 



"Wing. 



Tarsus. 



No.118689 9 ad. August 4, 1890, St. Paul, W.P 



No. 118688 d ad.July 30, 1890, St. Paul, W. P 



No. 151625 9 ad.July 29,1895, St. George, D.W.P.jr . 



8.92 

 9.02 

 8.50 



1.60 

 1.77 

 1.40 



1.55 

 1.50 

 1.40 



Order LOI^GIPENNES. Long-winged Swimmers. 

 Family STERCORARIIDAE. Jaegers. 



Three of the four American members of this family occur casually on the islands. 

 Possibly they are more numerous during the migrations. They breed northwards. 



29. Steroorarius pomariuus (Temm.). Pomarine Jaeger. " Baz-hoi-nik." 



Stercorarius pomatorhinus, CouES, in Elliott's Rpt. Aff. Alaska, 1873; Reprint, 1875, 196; Key, 



1890, 735.— Ellioti', Mon. Seal Ids. 1882, 132.— Saunders, Cat. B. Br. Mus. 1896, 322. 

 Stercorarius pomarinus, Townsend, Cruise, Corivin, 1887, 98. — A. O. U. Ch. List, 1895, 14. — 

 KiDGWAY, Man. 1896, 22. 

 A rare visitor. Elliott found one "perched in a listless attitude on the high, 

 mossy uplands between Kamminista and Polovina Sopka." Mr, 0. H. Townsend 

 obtained another on the same island. During the summer of 1890 two were seen on 

 St. George eating the carcass of a fur seal. One of these was killed and preserved 

 by Mr. Ed. Lavender. :So. 6l'522, ad. 5 , U.S.N.M., Juue 23, 1872, St. Paul, H. W. 

 Elliott, light phase. No. 106857, $ , Jiinel6, 1885, St. Paul, 0. H. Townsend. 



30. Stercorarius parasiticus (Linn.). Parasitic Jaeger. 



Stercorarius parfxsiticus, COUBS, in Elliott's Rpt. Aff. Alaska, 1873; Beprint, 1875, 196; Key, 

 1890, 736.— Elliot, Mon, Seal Ids., 1882, 132.— A. O. U. Ch. List, 1895, U.— Ridgway, 

 Man. 1896, 22. 



Stercorarius crepidaius, Saundeks, Cat. B. Br. Mns. XXV, 1896, 327. 



Casual. "I have seen but four or five examples of this species, which may be rated 

 as an infrequent visitor. It may be found upon the grassy uplands, where it will 

 alight and stand dozing in an indolent attitude for hours." — {Ulliott.) He found half- 

 digested berries of Umpetrwm in the stomachs. No. 02524, 2 , U.S.N.M., June 15, 1872, 

 St. Paul, H. W. Elliott, dark phase. 



31. stercorarius longicaudus Vieill^. Long-tailed Jaeger. 



Stercorarius laffoni, CouES, in Elliott's Rpt. Afif. Alaska, 1873; Beprint, 1875, 197; Key, 1890, 



738.— Elliott, Mon. Seal Ids. 1882, 132. 

 Stercorarius longicaudus, A. O. U. Ch. List, 1895, 15.— Ridgway, Man. 1896, 23. 

 Stercorarius parasiticus, Saukdbrs, Cat. B. Br. ilus. XXV, 1896, 334. 

 Seldom seen. "The specimen in my collection is one of the only two I ever 



