Jan., 1909. Birds of Illinois and Wisconsin — Cory. 



299 



Genus STERNA Linn. 



23. Sterna caspia Pallas. 



Caspian Tern. 



Sterna tschegrava (Lepech), A. O. U. Check List, 1895, p. 23. 



Distr.: A nearly cosmopolitan species; in North America breed- 

 ing along the middle Atlantic and Pacific coasts and in parts of the 

 interior. 



Adult in spring: Entire top of head, black, the black extending 

 below the eye; the occipital feathers, lengthened, extending to the 



Caspian Tern. 



nape; back and' wings, pale pearl gray; rest of plumage, white; pri- 

 maries, ash gray; no white on inner webs; bill, red; feet, black. 



Adult in winter, and in summer after the breeding season: Similar, 

 but has the head streaked with black and white. 



Immature: Differs in having the head spotted and streaked with 

 black and white, the upper parts more or less marked with brown 

 and dusky ; tail with irregular bars of black. 



Length, about 20 to 23.50; wing, 15.25 to 17; tail, 5 to 6.25; tar- 

 sus, 1.50 to 1.60; bill, 2.60 to 2.90; depth of bill at base, about .90. 



The Caspian Tern occurs casually on Lake Michigan in summer 

 and occasionally in winter, and has been found breeding on islands in 

 Green Bay, Wisconsin. The nest is merely a depression in the sand 

 with little or no lining. The eggs are 2, dull white or whitish with 



