22 NORTH AMERICAN BIRDS. 



slate, with a plumbeous cast in certain lights. Young : Entirely sooty slate, 

 the lower parts more or less barred with buff. [Note. — The above so-called 

 light and dark " phases'' represent the normal extremes of coloration. These 

 extremes, which are represented in comparatively a small number of speci- 

 mens, are connected by every possible intermediate condition of plumage, 

 specimens approximating to the lighter extreme, but differing in having the 

 lower parts (especially chest and sides) and nape more or less barred with 

 dusky, being most numerous.] Length about 20.00-23.00, wing 13.50-14.00, 

 middle tail-feathers 8.00-9.00, culmen 1.45-1.75, tarsus 2.00-2.10, middle toe 

 1.60-1.75. Eggs 2.35 X 1-63. Sab. Northern portions of northern hemi- 

 sphere, along sea-coasts and larger inland waters, breeding far northward ; in 

 America, south, in winter, to New Jersey and the Great Lakes. 



36. S. pomarinus (Temm.). Pomarine Jaeger. 

 a 1 . Culmen less than 1.45, tarsus less than 2.00, wing usually less than 13.50 ; 

 lengthened middle tail-feathers narrow and pointed at ends. 

 b x . Length of nasal shield, from base of unguis to frontal feathers, decidedly 

 greater than from the former point to tip of upper mandible. In freshly- 

 killed or living specimens, tarsi black, like the feet. Light phase, adult : 

 Top of head and lores grayish brown ; rest of head, neck, and lower 

 parts white, the lower tail-coverts grayish, the head and neck tinged 

 with straw-yellow ; upper parts uniform slaty. Young : Head and neck 

 streaked with dusky and buffy, the latter usually predominating ; lower 

 parts barred or spotted with the same ; upper parts dusky, the feathers 

 bordered terminally with pale fulvous or buff. Dark phase, adult : En- 

 tire plumage uniform sooty slate-color, the quills darker. Young : Pre- 

 vailingly dark brownish slate, wings and tail darker, the middle of neck, 

 all round, indistinctly streaked with whitish, and lower parts, except 

 chest and upper breast, barred with the same ; feathers of upper parts 

 narrowly tipped with bufty. Downy young (dark phase ?) : Uniform 

 silky grayish brown, lighter on lower parts. Length about 15.50-21.00, 

 wing 11.80-13.50 (12.67), longest tail-feathers 4.90-6.25 (5.40), culmen 

 1.15-1.40 (1.27), tarsus 1.50-1.85 (1.70), middle toe 1.20-1,45 (1.34). Eggs 

 2.30 X 1-64. Sab. Northern portions of northern hemisphere, breeding 

 toward Arctic regions ; south, in winter, to New York, Illinois, Colorado, 

 and even coast of Brazil..37. S. parasiticus (Linn.). Parasitic Jaeger. 

 b 2 . Length of nasal shield, measured from base of unguis to frontal feathers, not 

 greater than the distance from the former point to the tip of the upper 

 mandible. In freshly-killed or living specimens, tarsi light bluish, in 

 marked contrast with black of feet. 1 Adult : 2 Top and sides of head 

 sooty black; rest of head and neck, including ear-coverts and nape, 

 straw-yellow, paler on throat; upper parts uniform smoky plumbeous or 



1 In dried skins this color usually changes to a light olive or yellowish, or in very rare instances becomes 

 so darkened that the line of demarcation cannot be detected. 



s So far as known, this speoies has no dark phase like S. parasiticus. 



