Jan., 1909. Birds of Illinois and Wisconsin — Cory. 553 



The Cowbird is a common summer resident throughout Illinois 

 and Wisconsin. The female builds no nest of her own, but deposits 

 her eggs in the nests of other birds, usually selecting that of some bird 

 smaller than herself. 



The Yellow Warbler, which is included in the list of desirable 

 species by the Cowbird mother to relieve her of domestic cares, often 

 gets the better of her undesirable visitor by building a second story 

 to her nest, thereby covering the despised egg. Instances are known 

 where the rightful owner, to avoid being forced to start an avian elee- 

 mosynary institution, was compelled to build a third and even a fourth 

 story to her nest before she was left in peace to attend to her own 

 family duties. Usually one, sometimes two, and rarely three or four 

 eggs are left to be incubated and the young reared by the foster 

 mother. A nest of the Scarlet Tanager, taken by Dr. N. Dearborn 

 at Fox Lake, 111., on June 14, 1903, contained the remarkable number 

 of six, well incubated Cowbird's eggs and none of the rightful owner. 

 When found, the female Tanager was on the nest. The eggs are dull 

 white, or pale buff, irregularly and thickly marked with brown, and 

 measure about .87 x .66 inches. 



Section of four-story nest of Yellow Warbler in which Cowbird's eggs have been deposited. 



