324 THE WATER-RAT OR WATER-VOLE. 



setting his traps in water-vole subways which he 

 mistook for mole-runs, finding out his mistake 

 when he came to look at his sets. 



The digging propensities of the water-vole do 

 not seem to be very well known, and the subways 

 may exist only in localities where the earth is 

 sufficiently soft to render their construction easy. 

 Many examples were under my observation in the 

 valley of the river Wharfe, near Burnsall village, 

 to which locality these observations are almost 

 entirely limited. 



PERIODICAL INCREASE. 



The water-vole population of any given locality 

 varies considerably with the seasons, as seems to 

 be the case with all wild creatures of the water-side. 

 In some localities they may for a season or two 

 become a veritable plague, infesting the water's 

 edge in thousands, and drawing all manner of 

 predatory birds to the vicinity. Such plagues, 

 however, are of short duration, and are usually 

 followed by a corresponding period of scarcity. 

 What is the cause of this it is difficult to con- 

 jecture. Disease does not appear to be among 

 the water-vole's foes, flood -waters taking the 

 place of it, and therefore their sudden disappear- 

 ance after a term of abundance is probably due 

 to migration. 



SOLITARY INDIVIDUALS. 



The case of the bank-beaver, which neither toils 

 nor spins, but which lives its life remote from its 

 fellows in a bank-burrow of its own, has its exact 

 counterpart in the world of the water-vole. One 

 regularly comes across old and solitary individuals 



