STERCORARIID.E THE SKUAS AND JAEGERS. 217 



/S. pomarinus. Occasionally the middle rectrices are nearly as 

 long and attenuated as in S. longicaudus, and in the plumage 

 there is sometimes hardly any difference between examples of 

 the two species. They differ constantly, however, in the form 

 of the bill and, in adult birds, in the color of the tarsi; a bird 

 with black tarsi and having the nasal shield (measured along 

 the culmen) decidedly longer than the terminal portion of the 

 bill (from the point to the anterior edge of the nostril) being 

 with certainty S. parasiticus, while an example in adult plumage 

 having pale bluish tarsi and the nasal shield not longer than 

 the terminal portion of the bill, is sure to be S. longicaudus. 

 It is scarcely probable that the two forms are conspecific, but 

 possibly they may interbreed to a slight extent, and thus pro- 

 duce hybrids. 



The Parasitic Jaeger is known as an Illinois bird only on ac- 

 count of its occasional occurrence on Lake Michigan during 

 winter. Its habits are not obviously different from those of 

 the Pomarine Jaeger (/S. pomarinus), as briefly described on 

 page 214. 



Stercorarius longicaudus Vieill. 



LONG-TAILED JAEGER. 



Popular synonyms. Arctic Jaeger; Button's Skua; Long-tailed Skua; Whip-tall food- 

 fishermen); Marling-spike (do.). 

 Stercorarius longicaudus VIEILL. Ncuv. Diet, xxxii, 1819. 157. STEJN. Proo. U. S. Nat. 



Mus. v, 1882. 42.-B. B. & B. Water B. N. Am. ii, 1884. 339.-A. O. U. Check List. 



1886. No. 38. RIDGW. Man. N. Am. B. 1887, 23. 

 Stercorarius longicaudatus DE SELTS, Faun. Belg. 1842, 156. 

 Lestris parasitica ILLIG. Prodr. 1811, 273 (nee Larus parasiticus LINN.). LESS. Man. 



ii. 1828. 388. Sw. & BICH. F. B.-A. ii. 1831. 430.-NUTT. Man. ii. 1834. 317. 

 Lestris parasiticus TEMM. Man. Orn. ed. 1815. 512. AUD. Orn. Biog. iii. 1835. 470. 



Synop. 1839. 333; B. Am. vii. 1844. 192, pi. 452. 

 Stercorarius parasiticus SAUND. P. Z. S. 1876, 330. RIDGW. Nom. N. Am. B. 1881. No. 



699. 



Larus crepidata BBEHM & SCHILL. Beit. Z. Vog. iii, 1822. 212 (nee BANKS). 

 Lestris buffoni BOIE. Meyer's Tasoh. iii, 1822. 212. DEKAT, N. Y. Zool. ii. 1844, 315. pi. 133, 



flg. 291. 

 Stercorarius buffoni CouES.Proc. Acad. Sci. Phila. 1863, 136; Key, 1872, 309; Check List, 



1873, No. 542; 2d ed. 1882, No. 767; B. N. W. 1874, 615. 

 Stercorarius cepvhus STEPHENS, Shaw's Gen. ZooL xiii.1826. 211, pi. 23. LAWB. in Baird's 



B. N. Am. 1858, 840.-BAIBD, Cat. N. Am. B. 1859, No. 655. 

 Lestris microrhynchus BBEHM, Handb. Vog. Deutschl. 1831,726. 

 Lestris lessoni DEGL. Mem. Ac. B, Lille. 1838,108. 

 Lestris brachyrhynchus BBEHM. Vogelf, 1855,337. 



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