Enhancing Chances. 241 



owner. One disappeared before hatching, and so did 

 the owner's eggs, while two cow-bird's eggs were 

 hatched. At the age of three days one of the young 

 parasites disappeared, and only one left the nest of its 

 foster-parents. . . It is not unusual to find one or 

 more eggs of the rightful owner thrown out of the 

 nest, and it is supposed that the female cow-bird is 

 responsible for it. This is doubtless done to enhance 

 the chances of her own offspring. In other cases 

 there are minute punctures in the shells of the re- 

 maining eggs, and this is probably done on purpose 

 by the cow-bird, to keep them from hatching.-'^ 

 Major Bendire thus supplements Nehrling : 

 " There is no doubt that the cow-bird sometimes 

 throws the rightful owner's eggs out of the nest pur- 

 posely to enhance the chances of its offspring coming 

 to maturity. I have yet to see a punctured cow- 

 bird's egg. . . . One would naturally suppose that 

 birds breeding in holes in trees or under rocks would 

 be exempt from this infliction, but this it not the 

 case. Mr. G. W. Smith, formerly of Loveland, 

 Colo., writes me that he found a cow-bird's egg in a 

 rock-wren's nest which was placed under a ledge of 

 rock fully two feet from the entrance, and which was 

 barely large enough for the wren to squeeze through. 

 The dwarf cow-bird," adds Major Bendire, " which 

 usually selects nests of small birds for its eggs, is a 

 more persistent puncturer of foster-birds' eggs than 

 even the others." 



Mr. W. A. White, of Mathews, Va., especially 

 watched a nest in which he had dropped a cow-bird's 



* Nehrling, ii, pp. 244-5. 



