The House-Mouse (Mus musculus) in Corn Ricks

Abstract

In Britain the house-mouse lives mainly in grain ricks and buildings. Populations in country areas alternate seasonally between a high density, while the grain ricks are occupied, and a low density, while living in the fields when all ricks have been threshed, though there are a few mice living in the fields at all seasons. Figures on population density from the Oxford neighborhood show that badly infested ricks may contain from 1.4 to 14 mice per cu. m. By Jan. > 90% of ricks are infested. The size of population rises rapidly in the autumn after the ricks have been built, reaching a peak in the spring; after a rick is 8 months old there is little, if any, increase in the mouse population. Counts of mouse-holes in the sides of ricks show that in wheat there is a fairly constant relation between the number of holes and the number of mice. Oat and barley ricks are presumably too loose for any such relation to be established. Break-back trapping in and around grainfields proved that the house-mouse is the 3d commonest small mammal living in the fields. During winter the field populations are small, but by spring, possibly increased by large numbers released from ricks at threshing, more of them are found in the grainfields. They have now started to breed at quite a high rate. By the summer this field population is more than sufficient to reinfest the new ricks as they are built. Though house-mice rarely come out of ricks once they have settled in, their range within the rick is considerable, and most of the population visits the external surface of the rick, as proved by poison-baiting expts. in the sides of the rick, which sometimes killed 90% of the population. The amt. of damage done by house-mice in grain ricks is given by the % of tailed grain in the total yield at threshing.