388 



Biology in America 



lying nearby. Somewhat akin to liis feelings may have been 

 those of the farmer after sliooting the hawk which he thought 

 liad been preying upon his chickens, only to find in its talons 

 a rat, which was the real culprit. To kill a hawk is, in the 

 minds of most of us, a laudable act, for are not all hawks 

 "hen hawks," the inveterate enemies of the poultryman and 

 of smaller creatures of their own kind? So at least tliought 

 the farmers in the Humboldt Valley in Nevada, which in 

 1907 was visited by a plague of mice, which ate up every- 



Eed-tailed Hawks 

 One of the commoner ' ' hen hawks ' ' of the farmer, from an ilhistra- 

 tion by Louis Agassi/. Fuertes. 



Coiirttn!/ of the U. S. ISurciiu of Biological Survcp. 



thing in sight, gnawing the bark from fruit trees, burrowing 

 in the alfalfa fields and destroying the potatoes and other 

 crops. Out of 20,000 acres of alfalfa, 15,000 were so badly 

 damaged that they had to be ploughed under. At the heifdit 

 of the plague in November, 1907, it was estimated that there 

 were from 8,000 to 12,000 mice to every acre, while the total 

 loss to the valley was estimated at $300,000. Such mouse 

 plagues are no new occurrence. Numerous outbreaks of these 

 pests have occurred in Europe at various times, their num- 

 bers sometimes becoming so great that the simple-minded 

 peasants half believed that they had been rained upon them 

 from the clouds. 



