8 THE IMPORTANCE OF BIRD LIFE 



is generally supposed. Social species, those that 

 live in flocks, are particularly subject to its rav- 

 ages. Thousands of crows die each year in a 

 single roost from the effects of a virulent throat 

 and nostril malady which may possibly wipe out 

 fhe entire community. There is a "grouse dis- 

 ease" in Great Britain which has accounted for 

 tens of thousands of game-birds. Others are 

 attacked by a form of tuberculosis, and great 

 numbers of sandpipers each spring are left behind 

 on their northerly migration from South America 

 because of diseased sexual organs. 



Changes of climate and storms also take an 

 appreciable tolL It has been said by more than 

 one good authority that an icy winter kills more 

 game-birds than all the human hunters combined. 

 This statement, in the present day of millions of 

 eager gunners, perhaps is stretching the actual 

 facts, but there is no reason to doubt that entire 

 coveys of bob-white quail and other gallinaceous 

 fowl are frozen stiff in cold, sleety weather. Land 

 birds driven to sea by storms during their migra- 

 tions have been known to succumb in thousands. 

 This is one of the causes, though probably not the 

 true one, given for the sudden disappearance of 

 the passenger pigeon. Still other birds, unable to 

 migrate south in the wintei* because of disease, 

 injury, or old age, starve to death. 



Certain species do not leave the temperate cli- 

 mate in which they are born. In the winter 



