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THE UNIVERSITY OF THE STATE OF NEW YORK 



that we see. It is believed that elaborate nests like those of the 

 oriole have been gradually evolved from the simpler types. The 

 earliest birds, like their reptilian ancestors, probably did not 

 build nests but like turtles and like the mound birds of Australia 

 today buried their eggs in the sand or in heaps of decaying vege- 

 tation. With the great change from a cold-blooded to a v^^arm- 

 blooded condition of birds came the need for maintaining the 

 eggs at a constant temperature and incubation started. The 

 eggs were then laid on the surface of the ground or in holes in 

 trees where the bird could cover them. Those birds that laid 

 their eggs on the ground found it more comfortable and safe to 

 lay them in a depression and then to line the depression with 

 grasses or leaves. But the eggs were subject to the wet and 

 cold and some species then evolved nests that were built up from 

 the ground on piles of leaves, etc. The next step was the build- 

 ing of the nest in a bush or tree. Some species learned how by 

 laying twigs in the forks of trees they could build crude pla.tforms 

 that would hold their eggs and keep them above the flood and 

 their terrestrial enemies. Gradually the instinct to build more 

 and more complicated nests in the branches of trees arose until 

 finally we have such elaborate nests as those of the oriole sus- 

 pended from the tip of a branch or ornamented nests like those 

 of the hummingbird and pewee. Trace this probable evolution 

 in the series of pictures selected to illustrate this topic. 



Nighthawk, no nest 



Killdeer, simple depression 



Spotted sandpiper, some lining 



Vesper sparrow, nest well lined 



Virginia rail, nest built up from ground 



Black-crowned night heron, crude nest in tree 



Black-billed cuckoo, crude nest with slight 



lining Nu CvB2 



Catbird, well formed nest of sticks with con- 

 siderable lining Nu Cd2 



Song sparrow, nest of finer materials, well 

 formed, deep with soft lining Nu SpR2 



Wood thrush, nest with middle layer of plas- 

 tered mud 



Barn swallow, fully plastered nest 



Goldfinch, entirely made of soft material 



Acadian flycatcher, semihanging nest 



Baltimore oriole, hanging nest 



Yellow-throated vireo, ornamented hanging 

 nest 



