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



35 



Spring. 



Black Tern. 



Fall. 



Immature: Upper plumage more or less mixed with buff and pale 

 brown; under parts, white; the sides, gray; usually more or less black 

 about the eye; shafts of the primaries, brown. 



During changes of plumage the head and under parts show mixed 

 black and white markings. 



Length, about 9.30; wing, about 8.25; tail, 3.80; bill, i to 1.20; 

 tarsus .50. 



Immature birds are smaller. 



The Black Tern is a common summer resident in Illinois and 

 Wisconsin and breeds in both states, in May and June, usually pre- 

 ferring the smaller inland lakes. While it does occasionally eat small 

 fish, the greater portion of its food consists of insects such as dragon 

 flies and beetles, which it pursues and captures while on the wing 

 with great dexterity, turning and twisting in a manner suggesting the 

 flight of a swallow. The nest is built in a marsh or on the edge of 

 some grassy pond, and is composed of grass and reeds, sometimes a 

 mass of floating vegetation. The eggs are 2 or 3, pale olive brown, 

 heavily marked with chocolate. They measure about i.4ox i inches. 

 There are several sets of eggs in the Field Museum collection taken 

 at Fox Lake, Lake County, 111., June 6, 1903. 



Regarding its occurrence in Wisconsin, Kumlien and Hollister 

 say: "A very common summer resident in all the inland ponds, 



