378 



ELEMENTS OF GENERAL SCIENCE 



streams and lakes the black bass may produce hundreds of 

 eggs and guard them until the young are hatched and are 

 a few days old. After the mother fish has left her young, 

 she as well as other fish may catch and devour any of them 

 that are not so fortunate as to escape when pursued. In this 

 way not so much food is needed for young salmon and young 



FIG. 176. Struggle for existence among birds during the nesting period 



In the area shown in the photograph there were twenty-four nests containing 

 young birds or eggs. The parent birds range over a much larger area in secur- 

 ing food for the young birds, but it is evident that if all are adequately fed, 

 these young and old birds are important factors in the struggle for existence 

 in this locality. Also, since much of the food of these birds consists of insects 

 harmful to vegetation, the birds are important economic factors. The kind of 

 nest in each location follows : 1, brown thrasher ; 2, orchard oriole ; 3, robin ; 

 4, robin; 5, robin; 6, brown thrasher; 7, catbird; 8, catbird; 9, brown thrasher; 

 10, robin ; 11, orchard oriole : 12, cedar waxwing ; 13, robin ; 14, robin ; 7.5, king- 

 bird ; 16, brown thrasher ; 17, catbird ; 18, robin ; 19, robin ; 20, robin ; 21, cat- 

 bird ; 22, bronzed grackle ; 23, robin ; 24, robin. Photograph by C. W. Finley and 

 W. B. Morgan 



bass, because some of these fish have become food for others. 

 In any kind of living things the few that reach maturity are 

 to be looked upon as the ones that have been able to secure 

 enough food to nourish them and enable them to grow while 

 at the same time avoiding the catastrophe of serving as food 

 for some other hungry animal. 



390. Climatic dangers. An unexpected and severe storm 

 in early summer leaves in its path a mass of wreckage, as 



