350 HAWKS AND THE GROUSE DISEASE. 



prey of all kinds are very numerous, and are never 

 interfered with. No doubt hawks do kill many 

 valuable birds ; but if they do, they keep down the 

 excessive increase of voracious grain-feeders of many 

 kinds; and above all, they catch and destroy every 

 weakly or sickly bird. In this way we cannot doubt 

 they prevent epidemics among the bird tribes. It is 

 supposed by many thoughtful persons for example that 

 " the grouse disease " in England and Scotland, is the 

 result of the destruction of birds of the hawk tribe. 

 Sick birds thus became perpetuated, and disease 

 spread and has swept off many more grouse than 

 ever the hawks would have done. Grouse on the other 

 hand by over-preservation had become too numerous 

 and crowded and as we know one of the most certain 

 results of overcrowding of man, animals, or fowl, is 

 the occurrence of epidemic diseases. 



Wherever large numbers of creatures in a state of 

 nature are crowded together, the whole experience of 

 history shows that devastating epidemics are certain 

 to occur. Accumulations of dirt, where a few individuals 

 only are present are insufficient to produce plagues ; 

 but the moment population becomes numerous, poisonous 

 exhalations are evolved, food and water become 

 contaminated, and pestilence breaks out. The only 

 reason why the plague no longer visits London, as it 

 always used to do up to 1665, is because of artificial 

 sanitary precautions, adopted by man, as the results 

 of his experience on being visited with the consequences 

 of neglect of such safeguards. 



Birds and animals therefore, which adopt no such pre- 

 cautions, ought to be, and indeed are peculiarly liable 

 to outbreaks of various kinds of very fatal diseases. 



