ere eee ATU DSU Bh OFN | BU Ur Belin 13 
Natural Enemies of Birds 
IN A STATE OF NATURE the natural enemies of any species are as essential 
to its welfare as are food, water and air. That this is true is well known to 
biologists, but many people are slow to realize the fact. They see only the 
apparent damage to a species and do not recognize that there is also a 
beneficial effect upon the species preyed upon. 
The strong sentiment for protection of game birds has resulted in many 
cases in an attempt to exterminate their enemies. Hunters, sportsmen and 
gamekeepers persecute all creaturs that kill birds or dstroy their nests or 
young. With the increasing number of game and bird preserves it is more 
than possible that the destruction of so-called “vermin” may be overdone 
and that serious consequences may follow. The great scheme of nature 
requires insect-eating, fish-eating and flesh-eating birds and animals to 
serve as a check upon the increase of other species. These in turn have a 
certain controlling effect on vegetation, and thus is life on this planet 
regulated. 
Nature, in the effort to prevent the extinction of any species, tends to 
produce an excess of offspring and thus increase its numbers. The rate 
varies with different animals, but if this increase were to be unchecked they 
would multiply to the point where the food supply would be exhausted and 
the species die of starvation. Or, if the food habits should change, as they 
sometimes do under emergency conditions, they would interfere with others 
to the point where all would become extinct, either from starvation or from 
the diseases that result from crowding and weakness from shortage of food 
By disposing of surplus individuals their natural enemies prevent this, keep- 
ing the numbers low enough to prevent serious competition for food. Any 
species having an excess of food will increase rapidly and natural enemies 
are necessary to keep its increase below the limit of food supply. 
Natural enemies also act to preserve the fitness of a species in two ways: 
first, they act to prevent the spread of disease; second, by eliminating the 
weak and unfit they preserve the strongest, most active, most efficient, to 
carry on the species. 
Epidemics that occur among birds, just as they do among humans, are 
checked by the natural enemies which easily capture and destroy those 
weakened by disease, since such creatures act and react more slowly than 
do those not affected. Also, sick birds might be captured by enemies that 
would be too slow to take them if they were healthy and vigorous. The 
red-shouldered hawk, for instance, feeds mainly upon reptiles and mice, 
taking very few small birds, but if a bird should become slow and incautious 
from disease it might easily become a victim of the hawk. 
‘Professor Spencer F. Baird wrote on this subject many years ago as 
follows: “It has now been conclusively shown, I think, that hawks perform 
an important function in maintaining in good condition the stock of game 
birds by capturing the weak and sickly, and thus preventing reproduction 
from unhealthy parents. One of the most plausible hypotheses explanatory 
of the occasional outbreaks of disease amongst the grouse of Scotland has 
been the extermination of these correctives, the disease being most virulent 
