THE INSTINCT OF THE COWBIRD 



keen reasoning power, and would make chumps 

 of the others ; too senseless to know their own 

 eggs. In my observations, when the victim- 

 ized birds return and find the alien egg, they 

 exhibit great distress. 



My first study of the cowbird happened 



w 



BLUE -WINGED YELLOW WAHBLER. 



in an unexpected manner. I was watching 

 the nest of a pair of yellow warblers (Den- 

 droica (estiva) that contained two eggs. While 

 the owners were absent I saw a cowbird flutter 

 on to the nest and add her parasite egg to 

 its contents. When the yellowbirds returned 

 they at once discovered what had taken place, 

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