PARENT AND OFFSPRING 123 



Nests are built not only on trees, but also under 

 the eaves of houses. The swallows, for instance, 

 choose this situation for their artful homes, which are 

 constructed from little balls of earth collected by the 

 birds and mixed with bits of hay. 



The more highly developed a species, the more 

 helpless are the young at birth. This is a general 

 rule among all animals. All the birds of greater in- 

 telligence are born very immature, most of them 

 naked and some blind; and they are all completely 

 dependent upon their parents. The parrot, which 

 is considered the most intelligent of the birds, is 

 at birth the most immature of all. It cannot see 

 for eight days, and is unable to leave the nest for a 

 period ranging from thirty to fifty days, according 

 to the size of the species. The family life of the class 

 of birds last discussed is therefore much more pro- 

 longed than that of any others. 



It is not only in the nest-building and care of the 

 eggs that the birds show their parental affection. 

 Many duties lie before them after the young are 

 hatched; and the more highly developed the species, 

 the greater is the care bestowed upon the offspring. 

 Besides supplying the warmth that the young brood 

 needs, the parents shelter the nestlings from sun and 

 rain by spreading their wings over them. Even the 

 young of those birds that enter the world fairly mature 

 still need protection by the parents for a time. If 

 any danger is near, the parents exchange call-notes 

 that are recognized by the young from the first ; and 

 on hearing the call they shelter under the parents' 

 wings, or squat down. Sometimes, as in the case of 

 the plover and the partridge, the mother will divert 



