IT THE STRUGGLE FOR EXISTENCE 33 



instead of a diminution of this prodigious procession, it seemed 

 rather to increase, both in numbers and rapidity ; and anxious 

 to reach Frankfort before night, I rose and went on. About 

 four o'clock in the afternoon I crossed Kentucky Eiver, at the 

 town of Frankfort, at which time the living torrent above my 

 head seemed as numerous and as extensive as ever. Long 

 after this I observed them in large bodies that continued to 

 pass for six or eight minutes, and these again were followed 

 by other detached bodies, all moving in the same south-east 

 direction, till after six o'clock in the evening. The great 

 breadth of front which this mighty multitude preserved Avould 

 seem to intimate a corresponding breadth of their breeding- 

 place, which, by several gentlemen who had lately passed 

 through part of it, was stated to me at several miles." 



From these various observations, Wilson calculated that 

 the number of birds contained in the mass of pigeons which 

 he saw on this occasion was at least two thousand millions, 

 while this was only one of many similar aggregations known 

 to exist in various parts of the United States. The 

 picture here given of these defenceless birds, and their still 

 more defenceless young, exposed to the attacks of numerous 

 rapacious enemies, brings vividly before us one of the phases 

 of the unceasing struggle for existence ever going on ; but 

 when we consider the slow rate of increase of these birds, 

 and the enormous population they are nevertheless able to 

 maintain, we must be convinced that in the case of the 

 majority of birds which multiply far more rapidly, and yet 

 are never able to attain such numbers, the struggle against 

 their numerous enemies and against the adverse forces of 

 nature must be even more severe or more continuous. 



Struggle for Life heticeen closely allied Animals and Plants 

 often the most severe. 



The struggle we have hitherto been considering has been 

 mainly that between an animal or plant and its direct enemies, 

 whether these enemies are other animals which devour it, or 

 the forces of nature which destroy it. But there is another 

 kind of struggle often going on at the same time between 

 closely related species, which almost always terminates in the 

 destruction of one of them. As an example of w^hat is 



D 



