THE COMMON GRASS MOUSE 449 



mice live together in pairs/ or at all events have some sense of 

 property in their nests. They have also some sense of sanita- 

 tion, since they deposit their ordure in little heaps at particular 

 places, as at the mouths of their burrows. The rest of their 

 life-history is soon told. Although not incapable of climbing, 

 and extremely agile without being fast, they never under 

 normal circumstances leave the ground, and may be seen 

 running, but not bounding or jumping, to and fro in their 

 haunts, or sitting at little bare places at the mouths of their 

 burrows, at almost any hour of the day ; and no doubt they are 

 equally active at night. They probably spend their time 

 alternately in short sleeps and meals, their light slumber 

 guarding against surprise. They are quite capable of amassing 

 stores of food for winter use, always of such provender as will 

 keep, but for obvious reasons this propensity is not very highly 

 developed in the comparatively mild climate of England. 



They are copious drinkers and their appetite is enormous, 

 Dr Henry Laver having ascertained^ the weight of clover 

 consumed by a single captive individual in one day to be six 

 drachms (apothecary's weight = 2.3 grammes). 



They are very attentive to their fur, cleaning it carefully 

 after the manner of a cat. 



At intervals, either owing to favourable weather* — moist 

 summers and mild winters resulting in exceptionally nourishing 

 vegetation — but perhaps occurring independently in a natural 

 cycle, the numbers of Grass Mice undergo a very exceptional 

 increase, beginning gradually and extending over several years 

 if unchecked. More litters, and those of abnormal size, make 

 their appearance, and presently the usual equilibrium between 

 mice and vegetation is upset, the grass is all consumed, the 

 mice, usually in autumn, begin to stray into woods, bark* 

 trees, cut their roots, otherwise cause damage, and people 

 become aware that it is a "vole year" or that there is a 

 "plague" of mice. With the increased numbers there ensues 



' Adams has taken 73 males to 24 females, a proportion of, roughly, 3 males to i 

 female; but the figures, although suggestive, are too small to form the basis for a 

 definite statement as to the relative numbers of the sexes. 



2 Zoologist, 1881, 461. 3 R. Service, Ann. Scott. Nat. Hist., 1892, 134. 



* Charles Oldham {Zoologist, 1890, 98) once observed them engaged in barking 

 hollies. 



