The Rat and Mouse Populations of Corn Ricks

Abstract

A survey was made, 1939-41, of the number of rats, Rattus norvegicus, and house mice, Mus musculus, found at threshing time (Aug.-July) in stacks (ricks) of grain (wheat, barley, oats, beans) in Oxfordshire and Berkshire. Records were obtained from 518 stacks in 266 different groups. During both yrs. the number of rats rose from late summer to a max. the following April and then declined as the rats scattered to fields and hedges. The av. max. number per stack in 1940 was 79 and in 1941 was 45. A higher % of 2 rats wintering (Nov.-Feb.) in the stacks were pregnant (28%) than of [male] wintering elsewhere (3%). Information obtained on mice was less accurate but indicated them to be an equally serious economic problem. In the same stack, rats tended to concentrate in the upper half and mice in the lower half. Practical recommendations are to thresh as early as possible to prevent a build-up of the population and to kill all rats at the time of threshing to prevent spread elsewhere.