OF EASTERN PENNSYLVANIA. 357 



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set to work and completely cover it by an addition 

 to the inside of the nest. 



As a general thing, the Cowbircl deposits her 

 eggs in the nests of birds smaller than herself; 

 but this is not always the case as instances are 

 recorded where they were dropped into the nests 

 of Tnrdus niustclinus and Sturnella magnet ; but 

 we have never discovered any such cases. Why 

 the smaller birds should be the recipients of such 

 unsolicited favors, it is difficult to guess, unless the 

 cowardly spirit of the species under consideration, 

 operates to prevent similar discourtesies being 

 shown where they would probably be resented. 

 As a proof of such cowardice might be cited the 

 stealthy manner in which the Cowbird approaches 

 the nest of any of the foregoing species. She is 

 ever on the alert for fear of detection. In case of 

 discovery, she takes to flight, often failing to ac- 

 complish her wish; but when suddenly pressed, 

 she is constrained to drop her egg, thus account- 

 ing for the fact that eggs are frequently seer, 

 upon the ground, either entire or broken. 



It is said that the eo-o- of the Cowbird hatches 



<_>o 



rather sooner than those of the species among 

 which it is found, and from this it is argued by 

 some that it is a wise provision of nature, which, 

 were it otherwise, would defeat the end which she 

 had in view. Experience has taught us that a set- 

 ting of eggs is sometimes longer in hatching than 

 others. The difference of time is evidently clue 

 to variation in the amount of heat to which the 



