182 



a spurious egg in its nest. Birds^ except in unusual in- 

 stances, cannot count, but they must recognize the difference 

 in sizes between the eggs. Usually they accept the odd one 

 without protest but instances often occur when a little bird, 

 wiser than others of her kind, rolls the undesired egg out of 

 the nest or builds another bottom to her nest, sacrificing her 

 own eggs with the one of the Cowbird. 



Fig. 156. YELLOW-THROAT ON NEST. 



In this instance, the little Yellow-throat laid two more 

 eggs of her own and the nest would hold no more. As usual, 

 the Cowbird egg, probably because it is larger and receives 

 more warmth from the sitting bird, hatched a day before the 

 smaller eggs. I passed by the nest and watched the pro- 

 gress of the young nearly every morning. Male and fe- 

 male Yellow-throat were very busy feeding the little birds ; 

 the young Cowbird, because of his larger size and much 

 larger appetite, received food twice to every once for the 

 rightful occupants of the nest. Young Maryland Yellow 



