13 



when the eggs of the ground birds are in the nest, and thus so 

 occupying its attention and attracting it away from birds- 

 egging as to save many early broods of birds. 



The marsh hawk (Circus hudsonius) feeds to some extent 

 on marsh birds and their young, but a much larger part of 

 its food consists of meadow mice and frogs. These mice cer- 

 tainly would be very destructive to young birds were they 

 not held in check, and large frogs are known to swallow the 

 young of water birds. Marsh hawks and other enemies prevent 

 many frogs from reaching a size when they would be danger- 

 ous to young birds. 



The larger hawks feed commonly on snakes, which are known 

 to be destructive to birds. Even the rattlesnake is a common 

 prey of the large red-tailed hawk (Buteo borealis). 



NATURAL ENEMIES TEND TO KEEP THE NUMBERS OF 

 BIRDS AT THEIR NORMAL LIMIT. 



Under natural conditions, wherever man and his satellites — 

 cats, rats, dogs, hogs, goats, etc. — have not interfered with 

 the balance of natural forces the native natural enemies of 

 birds do not tend, on the whole, to reduce the numbers of any 

 species to a point much below that at which its natural food 

 supply will maintain it. Any species having a bountiful food 

 supply constantly tends to increase rapidly in numbers, and 

 natural enemies and meteorological checks are necessary to 

 keep its increase below the limit of its supply of food. If for 

 any reason these forces were unable to do this, and a species 

 became too numerous, starvation and disease would follow. 



A school of writers has risen of late who refer to the natural 

 enemies of birds as far more destructive than the hunter, and 

 assert that it is useless to attempt to protect birds and increase 

 their numbers anywhere unless natural enemies (which they 

 denominate as vermin) be first destroyed. It even is asserted 

 positively that if a certain tract of land be set aside, and all 

 shooting upon it be stopped for a series of years, the game 

 and birds will lessen rather than increase, because of the un- 

 restrained destructiveness of their natural enemies. This con- 

 tention apparently is not supported by facts. 



If we go back to the times of the early settlers we find that 



