THE VIREO AND THE COWBIRD 131 



first egg might spoil before the last one was laid. 

 So the families would be very small, and the 

 inevitable result would be a speedy extermination 

 of this useful bird. To avoid this, the bird lays 

 her eggs in the nests of other birds, usually choosing 

 the homes of birds rather smaller than herself, so 

 that her young shall be under no disadvantage in 

 point of size. Sometimes she deposits her egg in 

 the nest before the rightful owner has commenced 

 laying. In such cases they are seldom allowed to 

 hatch, but more often the cowbird watches her 

 opportunity and places her eggs in a nest that 

 already contains one or more. Then it is hatched 

 with the others, and the young cowbird, being 

 nearly always larger than his companion nestlings, 

 manages to secure the greater share of the food 

 and thrives accordingly, while the rightful owners 

 sometimes die (so I am told) in the nest, or are 

 forced out of it to die on the ground. All this is 

 done by the cowbird in self-defence, and we should 

 hesitate before condemning the bird for its seem- 

 ingly strange behaviour. 



A few years ago I had an opportunity of watch- 

 ing a pair of red-eyed vireos who had selected a 

 tree near our house for their nesting site. The nest 

 I had watched from its very beginning a few 

 beakfuls of dry grass and fine bark woven about 

 the fork of a horizontal branch. Day by day the 

 nest grew until after five days the beautiful 

 semi-pensile structure was complete. It was a 

 simple basket-like nest, supported by its upper 

 edges being led to the forked branch. There was 

 no attempt at decoration of any kind such as we 



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