ARVICOLA RIPARTUS^ 2/3 



operation of the same cause, come to be surrounded by slowly-grow- 

 ing dome-shaped chambers. These increase in size until the spring- 

 thaws, in March and April, melt away their roofs, thus admittino- the 

 light and cold. They are then deserted. During snow-shoe tramps 

 over the iields at this season 1 have often noticed holes, from a few- 

 inches to a foot in diameter, appearing as if sharply cut in the surface. 

 On inspection, they invariably proved to be the summits of these 

 dome-shaped cavities, and a nest was always found at the bottom of 

 each, surrounded b\- a zone of bare ground. They ranged froni one 

 to two feet (approxiniately 300 to 600 mm.) in diameter, and most of 

 them were two feet in height. b>om the bottom of each chamber 

 numerous runways and burrows penetrated the snow in all directions. 

 Some followed along directly upon the ground, while others sloped 

 upward at various angles. Many ran horizontally at varying levels, 

 resting upon the dense strata that indicated the surface lines at 

 different times during the winter. Near each nest was one or more 

 burrows that reached the surface and contained considerable accumu- 

 lations of the animals dejections. These seemed to be watch holes 

 where the Mice came regularly to look at the prospect outsitle. 



Meadow Mice sonietimes, but not often, travel upon the snow, and 

 they occasionally stray so far that they are unable to Imd tlu! holes 

 through which they came up. If this happens when there is a hard 

 crust, through which they cannot burrow, they wander aimlessly about 

 for a while and finally perish from the cold. In Martli and April I 

 have several times found them frozen to death upon the crust. 



They are always present in greater or less numbers, but are 

 not often sufficiendy abundant to direct the attention of the farmer 

 to their depredations. Occasionally, however, they multiply to such 

 an alarming extent that the niost su[)erficial observer is impressed 

 with the magnitude of their ravages. They devastate the meadows, 

 Q-rain-fields, and orchards of the farmer, and ruin the nurseries of the 

 horticulturist. Whether these periodical invasions are the result of 

 unchecked reproduction, or of migration, has not been positively 



