THE STRUGGLE FOR EXISTENCE 29 



from the young to check the increase of the species, and 

 maintain the balance of life which Nature desiderates. 

 " Let us again consider the case of carnivorous birds, 

 where the parents do not devour their own offspring. 

 Let us take the eagle as representative of the raptorial 

 group. These birds in Europe build their eyries upon 

 mountain ranges, and each pair exercises a jealous 

 dominion over a certain area in which it will allow 

 no other pair to settle it may be a valley or part 

 of a valley. A well-known haunt of the eagle is in 

 the mountains of Norway, where they breed and 

 maintain their numbers from generation to generation 

 without ever increasing. Though not prolific birds, 

 they might easily treble their numbers in a generation, 

 and if they had an unlimited amount of unoccupied 

 territory to settle in, they would do so. But their 

 territory has all been occupied for ages. What then 

 prevents their multiplication ? It is well known 

 that the male and female birds are both excellent 

 parents, solicitous for the well-being and proper 

 upbringing of their young, until they are able to 

 fly abroad on steady wing and forage for themselves. 

 The old birds then drive them forth from the eyrie, 

 with sentence of death passed upon them should they 

 attempt to return. The birds thus driven away from 

 the parental nest will not be permitted to effect a 

 settlement in any haunt where the pair in possession 

 are able to kill them. On the other hand, they will 

 take possession of haunts that are deserted from the 

 old possessors being dead, and of haunts whose occu- 



