JAX., 1909. BIRDS OF ILLINOIS AND WISCONSIN CORY. 291 



visitor to the northern part of the state." (A. W. Butler, Birds of 

 Indiana, 1897, p. 571.) "A regular and not uncommon winter resi- 

 dent on Lake Michigan." (Nelson, Birds N. E. 111., 1876, p. 145.) 

 "A regular winter visitant on Lake Michigan, but by no means com- 

 mon, although occurring more frequently than glaucus." (Kumlien 

 and Hollister, Birds of Wisconsin, 1903, p. 9.) 



15. Larus marinus LINN. 

 GREAT BLACK-BACKED GULL. 



Diitr.: North Atlantic ocean, south in winter to the middle states 

 and the Great Lakes, and occasionally much further south (accidental 

 in Florida). 



Adult in summer: Whole back, dark slate color; outer primaries, 

 black (slaty black when held in the light), tipped with white; head, 

 tail, and under parts, white; bill, chrome yellow, with red spot on 

 lower mandible. 



Adult in winter: Similar, but with head and neck streaked with 

 pale brownish gray. 



Immature: General plumage mottled and streaked with gray and 

 pale brown, many feathers with pale edges; primaries, brownish black, 

 the inner ones narrowly tipped with white; bill, blackish. 



Length, 28 to 31.50; wing, 17.50 to 19.50; bill, 2.42 to 2.55; 

 greatest depth of bill, .92 to 1.05. 



Although apparently not very common, this species occurs on 

 Lake Michigan in the late fall and winter. "Not an uncommon 

 winter resident upon Lake Michigan. The immature young are 

 greatly in excess of the adult." (Nelson, Birds N. E. 111., 1876, p. 

 145. ) "We have seen this well marked species on Lake Michigan at 

 the Milwaukee Light House, midwinter, 1 880-81, and on at least two 

 occasions, out on the Lake. It is, however, rare." (Kumlien and 

 Hollister, Birds of Wisconsin, 1903, p. 9.) 



16. Larus argentatus PONTOPPIDAN. 

 HERRING GULL. 



Larus argentatus Briinn., A. O. U. Check List, 1895, p. 18. 



Distr.: Nearly the whole of North America, south to Cuba in 

 winter; breeds from the latitude of Maine and Wisconsin northward. 



Adult in summer: Back, pale bluish gray, or pearl gray; primaries, 

 brownish black, more or less marked with white; rest of plumage, 

 white; bill, yellow, a red spot on lower mandible at the angle. 



