JAN., 1909. BIRDS OF ILLINOIS AND WISCONSIN CORY. 



47 



*GROUP 5. Wing, over 17 inches long. 



Primaries, marked with more or less black. Larus marinus. 



Great Black-backed Gull. 

 See No. 15. 



No black on primaries. Larus hyperboreus. 



Glaucous Gull. 



See No. 13. 



Subfamily STERNIN^. Terns. 



Upper mandible, nearly straight, not hooked or decidedly rounded 

 near tip; nostrils, in basal half of bill; outer tail feathers, usually 

 longer than middle feathers; toes, four; front toes, webbed; hind 

 toe, small, but well developed. 



Common Tern. 



*GROUP 1. Wing, 5.50 to 7.50 inches long. 



Forehead, white; bill, black; under parts, 

 white; back, pearl gray; crown, black (adult 

 in summer); back and crown, mottled (im- 

 mature). Sterna antillarum. 



Least Tern. 



See No. 28. 



*Por directions for measurement, see page 21. 



