BIRDS OF NEW YORK STATE 129 



6 Hole nesters 



The birds that elected to lay their eggs in the holes of trees 

 found it unnecessary to build nests and from the beginning have 

 never developed a nest-building instinct other than learning to 

 drill their own cavities. Later on some birds that had developed 

 a nest-building instinct in the open, discovered that their eggs 

 were much safer in the cavities in trees or banks, than in open 

 nests, and took to building their nests in such places. In spite 

 of the fact that nests are unnecessary in such places, they still 

 retain the nest-building instinct and build elaborate nests at the 

 bottom of the cavity. 



a The original type, at bottom of hole, no structure 



Downy woodpecker Nu WpD2 



Sparrow hawk Nu HT3 



b Reversion to hole nesting, nest at bottom of hole 



Bluebird Nu Bm3 



Chickadee Nu Ci3 



7 Degenerate nesters — parasitism 



Cowbird's eggs in vireo's nest Nu ViB2 



Cowbird's eggs built upon by vireo Nu ViB3 



Young cowbird hatched by vireo Nu ViB4 

 Yellow-billed cuckoo egg in black-billed 



cuckoo nest Nu CvB4 

 Eggs 



The eggs of birds are among the most beautiful objects in all 

 nature. It is little wonder that the instinct of the small boy in 

 response to the appeal which they make to his eye leads him to 

 make an egg collec,tion. In presenting the following study effort 

 should be made to interest children in the manner in which the 

 parent birds care for their eggs and in the young which hatch 

 from them and to discourage in every way the making of egg 

 collections. What the egg is in and what is in the egg are more 

 important interests than mere form, color and size of the shell. 



1 Number 



The number of eggs laid by an individual is fairly constant 

 for each species. 



a Small 



Mourning dove, 2 eggs Nu DoM2 



Hummingbird, 2 eggs Nu HuR2 



5 



