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ANIMAL BIOLOGY 



few sticks on which to deposit its eggs; robins, sparrows, 

 warblers, and many other song birds build a more elaborate 

 nest which is usually lined with soft materials which tend 

 to preserve the warmth of the eggs and young. As a 

 rule, primitive birds build crude nests, while birds of a 

 higher type take more care in providing for the safety 

 and comfort of their progeny. 



There are a few birds such as the cuckoos and cow birds 

 whose young live at the expense of other species. The 

 eggs of the European cuckoo, for instance, are laid along- 



FIG. 153. Male bluebird with grasshopper. (After Forbush.) 



side of the eggs of other birds and the young cuckoo is 

 fed by the rightful owners of the nest like one of their own 

 young. When the young cuckoo develops sufficient 

 strength it has the peculiar instinct of pushing its com- 

 panions out of the nest, where they frequently perish. 

 Notwithstanding this conduct, which seems like the basest 

 of ingratitude to its benefactors, the birds continue to 

 care for the young interloper until it is ready to take flight. 

 One of the most pleasing associations with the advent 



