WATER BIRDS. 47 



This species nests only in high latitudes, mainly or entirely within the 

 Arctic Circle, and its eggs are laid singly on islands and often on the bare 

 rocks of cliffs overhanging the sea. The eggs average 1.90 by 1.29 inches, 

 and are greenish white in color. 



TECHNICAL DESCRIPTION. 



The adult in summer has the head and neck all around, together with upper parts, blue- 

 black, more glossy above, duller and more brownish on the throat, chest and sides of head. 

 Scapulars white-edged and secondaries tipped with white. Under parts, except throat 

 and chest, pure white. In winter the brownish black disappears from the throat and 

 neck leaving the entire under parts pure white, and this color often extends over the sides 

 of the head and along the sides of the neck until it nearly meets on the back of neck. Length, 

 7.25 to 9.15 inches; wing, 4.50 to 4.75; culmen, .50. 



Order II. LONGIPENNES.— Long-winged Swimmers. 



KEY TO FAMILIES. 



A. Covering of upper mandible of three distinct pieces, hook, side-piece, 



and cere-like piece; two middle tail feathers projecting beyond the 



rest. — Family 4, Stercorariidae.- — Skuas and Jaegers (Gull-chasers), 



page 47. 



A A. Covering of upper mandible of a single piece; middle tail-feathers not 



projecting beyond the rest. — Family 5, Laridse — Gulls and Terns, 



page 49. 



Family 4. STERCORARIID.E.— Gull-chasers. 



KEY TO SPECIES. 



A. Projecting middle tail-feathers broad at tip. — Pomarine Jaeger. No. 8. 

 AA. Projecting middle tail-feathers narrow at tip. — Parasitic Jaeger. No. 9. 



8. Pomarine Jaeger. Stercorarius pomarinus (Temm.). (36) 



Synonyms: Jaeger Gull, Gull-chaser, Gull-hunter. — Larus pomarinus and Lestris 

 pomarinus, Temm., 1815. — Stercorarius pomarinus of most recent authors. 



Most likely to be recognized, if at all, through its habit of chasing other 

 sea-birds, somewhat in the manner of a hawk, although it seldom kills the 

 bird it pursues, being content usually to compel it to drop or disgorge the 

 prey which it has just captured. 



Distribution. — Seas and inland waters of northern portions of the North- 

 ern Hemisphere; south in winter to Africa, Australia and probably South 

 America. 



This is another sea-bird of wide distribution, but unlike the Auks it is 

 by no means restricted to salt water. Nevertheless it is seldom seen and 

 still more seldom captured on the Great Lakes. The only record for Mich- 

 igan which we have been able to verify is that of a specimen taken on the 

 Detroit River May 30, 1879, by R. Sanlier, and recorded by the late W. H. 

 Colhns in the Oologist for 1879, p. 24. This specimen is now in the Museum 

 of Comparative Zoology, Cambridge, Mass., and bears the following label: 



