34 BIRD FRIENDS 



Condition of young at birth. For the most part 

 the lower forms of birds are precocial, the young 

 being ready to walk when first hatched; the higher 

 forms are altricial, the young being helpless and re- 

 quiring the care of the parents. This constant care 

 of the young is a sign of advancement among all 

 animals. Probably the first birds were all precocial 

 and some gradually evolved the altricial habit. 



Time in nest. The time that the altricial birds 

 remain in the nest varies with the size of the birds. 

 In general the larger birds remain longer in the nest 

 than do the smaller birds. In the case of the song 

 sparrow, the young may leave the nest at the end of 

 a week, while some birds may remain several months 

 in the nest; but for most of our common birds the 

 time averages about two weeks. 



The following tables give in brief form some facts 

 regarding the nesting-habits of a few birds. These 

 figures represent observations made of a particular 

 pair of birds. Observations on other birds of the 

 same species would doubtless give different figures. 

 But these results give at least an approximate idea 

 of the time involved in these various activities. The 

 incompleteness of this table suggests how many 

 things are yet to be learned about the habits of our 

 common birds. 



The work of the parent birds in rearing their young 

 consists chiefly in three activities : feeding the young, 

 cleaning the nest, and brooding the young. 



