JAN., 1909. BIRDS OF ILLINOIS AND WISCONSIN CORY. 49 



Bill, red, tipped with black; feet, orange red; back, pearl gray or 

 gray and buff. Sterna hirundo. 



Common Tern. Wilson's Tern. 

 See No. 26. 



* GROUP 6. Wing, 13 to 17 inches long. 



Bill, orange or yellowish; tarsus, less than 1.50; inner web of 

 outer primary, usually with more or less white. Sterna maxima. 



Royal Tern. 

 See No. 24. 



Bill, red or reddish; tarsus, over 1.50; inner web of outer primary, 

 usually without white. Sterna caspia. 



Caspian Tern. 

 See No. 23. 



* GROUP 7. Wing, over 17 inches long. 



Bill, red or reddish. Sterna caspia. 



Caspian Tern. 

 See No. 23. 



*For directions for measurement, see page 21. 



