CLIFF-DWELLERS 35 



hills so that the young may find food in their 

 journey to the light of day. 



The skill shown by these birds in the construc- 

 tion of incubators for their eggs is most remark- 

 able when we consider that in the different parts 

 of the country where they range, the materials at 

 hand vary widely in kind and quality. Yet they 

 are uniformly successful. They are engineers of 

 great ability and ingenuity, and seem to know just 

 how and in what quantities to mix whatever ma- 

 terials the region affords. That they understand 

 in some measure the natural principles which they 

 employ is shown by the intelligent care they take in 

 the choice of vegetation and in the scrupulous re- 

 moval of all decayed matter of the previous year. 



Some mound-building birds band together to ac- 

 complish their work, and the fairness and good- 

 fellowship they show would put human labourers 

 to shame. They all join heartily in the task, and 

 the result proves the wisdom of co-operation. In- 

 deed these birds have solved many of the most seri- 

 ous and complicated problems of their existence in 

 a way that would do credit to human beings, and 

 their methods are not unlike those of man in the 

 early stages of development. 



