216 BIRDS OF ILLINOIS, 



three or four of them, they seemed to grow wilder. The Jaegers 

 while on the wing keep the tail widely spread, in the shape of a 

 fan, the long feathers, when the birds have them, being kept 

 close together." 



Stercorarius parasiticus (Linn.) 



PARASITIC JAEGER. 



Popular synonyms. Richardson's Jaeger (= dark phase) ; Teaser; Bosun; Marling-spike 

 (cod-fishermen). 



Larus parasiticus LINN. S. N. ed. 10, i, 1758, 136; ed. 12, i, 1766, 226. 



Stercorarius parasiticus SCHAFF. Mus. Orn. 1779, 62, pi. 37. LAWB. in Baird's B. N. Am. 

 1858, 839. BAIRD, Cat. N. Am. B. 1859, No. 651. COUES, Key, 1872, 309; Check List, 

 1873, No. 541; ed. 2, 1882, No. 766; B. N. W. 1874, 611. B. B. & R. Water B. ii. 1884,335. 

 A. 0. U. Check List, 188C,No. 37. RIDGW. Man. N. Am. B. 1887,22. 

 Lonis crepidatus BANKS, Hawkesworth's Voy. ii, 1773, 15. 



Stercorarius crepidatus VIEILL. Nouv. Diet. 1819, 155. SAUNDEKS, P. Z. S. 1876, 326. 



RIDGW. Norn. N. Am. B. 1881, No. 698. 



Lestris richardsoni Sw. & RICH. F. B.-A. ii, 1831, 433, pi. 73. NUTT. Man. ii, 1834,319. 

 AUD. Orn. Biog. iii, 1835, 503; Synop. 1839, 332; B. Am. vii, 1844, 190, pi. 452. 



HAB. Northern part of northern hemisphere ; south in America, in winter, to New York, 

 Illinois, and Colorado, and even to Brazil (Rio de Janeiro; fide SAUNDEBS, Jour. Linn. Soc. 

 xiv, 392). Breeds in the "Barren Grounds" of Arctic America. 



SP. CHAB. Adult, light phase: Entire pileum, with lores, grayish brown; rest of the 

 head, with entire neck and lower parts as far as the crissum, white, the head and neck 

 more or less tinged with straw-yellow. Upper parts uniform brownish slate, becoming 

 gradually darker on the primaries and tail. Crissum uniform brownish gray. "Bill grayish 

 black, the upper parts bluish; iris brown; legs and feet black." (AuDUBON).* Adult, dark 

 phase: Entirely uniform dark sooty slate, the remiges darker, nearly black termi- 

 nally. Young, light phase: Head and neck streaked with dusky brown and fulvous-buff, 

 the latter usually predominating; lower parts more or less distinctly barred, or spotted 

 transversely, with the same. Upper parts brownish dusky, all the feathers bordered ter- 

 minally with fulvous-buff. Young, dark phase: Prevailing color dark brownish slate, the 

 wings and tail darker. Middle of the neck, all round, indistinctly streaked with grayish 

 white; lower parts, except chest and upper parts of breast, barred with grayish white, 

 the bars broad and sharply defined on the crissum. Scapulars, interscapulars, wing- 

 coverts, upper tail-coverts, and feathers of the rump narrowly tipped with pale dull buff. 

 "Bill light blue, dusky at the end; iris brown; tarsi and basal portion of the toes and webs 

 light blue, the rest black" (AUDUBON). Downy young: Entirely silky grayish brown, 

 lighter on the under surface. 



Total length, about 18.50 inches; extent, 40.00; wing, 11.80-13.15 (average, 12.67); middle^ 

 tail-feathers, 7.70-10.25 (8.66). the lateral rectrices. 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). 



Between the extreme phases of plumage described above there 

 is in different specimens every possible intermediate coloration, 

 the individual variation being fully as great as in the case of 



*Accordingto MACGILLIVKAT (History of British Birds), the adult male in summer 

 has the bill grayish black, tinged with blue above, the base of the lower mandible slightly 

 llesh-oolored, andjthejfeet and claws black. 



