A KEY TO THE EGGS 



OF THE MORE COMMON BIRDS KNOWN TO BREED IN 

 NORTHERN ILLINOIS AND SOUTHERN WISCONSIN. 



GROUP 1 * WHITE EGGS (UNMARKED). 



SECTION I. NEST ON BRANCHES OF TREES OR 



BUSHES. 



PART I. EGGS LESS THAN .60 IN. LONG. 



Eggs 2. Size, about .50 x .35. Smallest of our birds' eggs. 



Trochiliis colubris. 

 Ruby-throated Hummingbird. 



PART 2. EGGS FROM .60 TO .85 IN. LONG. 



Eggs, 3 to 6. Size, about .66 x .48. Eggs usually showing faint 

 bluish tinge. Nest lined with thistle down, usually from 6 to 25 feet 

 from ground. Breeds, July and August. Bird: female, wings and tail, 

 dusky; under parts tinged with yellow. Male, bright yellow; crown, 

 wings, and tail, black. Astragalinus tristis, 



American Goldfinch. 



Eggs, 3 to 4. Size about .73 x .55. Eggs usually showing faint 

 bluish tinge. Nest not lined with thistle down, usually in crotch of 

 bush near ground. Breeds, May and June. Bird: female, grayish; 

 wings, dusky; no yellow on under parts. Male, blue; wing and tail, 

 mostly black. Passerina cyanea. 



Indigo Bunting. 



PART 3. EGGS BETWEEN .90 AND 1.25 IN. LONG. 



Eggs, 2. Size, about 1.08 x .83. Nest, a mat of loose twigs. 



Zenaidura macroura carolinensis. 

 Mourning Dove. 



PART 4. EGGS MORE THAN 1.50 IN. LONG. 



Eggs, 3 to 6. Size, 1.92 x 1.55. Eggs, sometimes dull white or pale 

 bluish white, but usually more or less faintly marked with pale brown. 



Accipiter cooperii. 

 Cooper's Hawk. 



* Eggs vary more or less in size and as the average measurements are given in this key, they 

 should only be considered as approximate. For example, if in a series of eggs of a certain specie's 

 the longest was 1.15 in. (measured on a straight line) and the shortest i.oo. the length here given 

 would be 1.08 in. 



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