522 Life-histories of Northern Animals 



If we make for our six common Mice a ladder to 

 show their chosen elevations, we shall put the Peromyscus 

 arcticus at the top, far above the ground, next the P. bairdi, 

 next the Evotomys, very near the ground, next Microtus 

 minor, a little below, and lowest of all, much of the time 

 below the surface, we find the present the most subterranean 

 of the group. 



HOME- The home-range of the individual is probably less than 



50 feet across. I have seen an isolated hollow of that size 

 which was obviously the whole world of a dozen or more of 

 these Mice. 



ABUN- This is generally considered the most abundant quad- 



ruped in Manitoba; even in the years when the Rabbits are 

 multiplied to millions, they fall far below the ordinary numbers 

 of this species. In a year of plenty it is common to hear of 

 half a dozen under each grain stook, or of a bushel being 

 killed at each threshing. I have heard of over a thousand 

 in one oat stack. I have seen over 1,000 (by guess) in a 

 field of 10 acres. I suppose that, reckoned with its kinsman 

 and complement, M. minor, the two together in their year of 

 apogee populate the whole of Manitoba at the rate of 10,000 to 

 the square mile. Merriam estimates^" that in the Adirondacks 

 during off years they number not less than 5,000 on a 200-acre 

 farm, which would be over 15,000 to the square mile, and I 

 have no reason to suppose them less abundant in Manitoba. 

 To exceed these numbers we must descend from the ranks of 

 quadrupeds and search among insects. 



This abundance is more or less periodic. The reasons 

 for the abnormal increase are as little known as the causes of 

 its disappearance. The analogous case of the Varying Hare 

 would lead us to attribute the destruction to some epidemic 

 disease. 



The Mouse millions are doubtless, as elsewhere noted, the 

 boats especially designed to bring food over from the Mainland 



*" Mam. Adir., 1884, p. 274. 



