Factors affecting the breeding of the field mouse ( Microtus agrestis ). Part III.—Locality

The first two papers in this series (1932,a andb ) were descriptions of experimental work. This third paper is based upon observation. In order to study the effect of latitude upon the starting and stopping of breeding, we chose three areas in a nearly north and south line. The most northerly was about 360 miles from the most southerly, and the other area was roughly half way between them. All three areas were elevated grassland belonging to the Forestry Commission, whom we must thank for their kind co-operation, without which the investigation would have been impossible. The most northerly area was at Huntly in Aberdeenshire. The intermediate area was at Newcastleton in Roxburghshire. The most southerly area was at Corris in Merionethshire (see fig. 1.). The Aberdeen and Roxburgh areas were at elevations of about 700 feet, and the Merioneth area at between 500 and 600 feet.Microtus agrestis was caught in each area as nearly as possible every month from January, 1930, to December, 1931. Deep snow and other causes occasionally prevented the monthly trapping in one or other area. On the average 32Microtus were caught each month during these tow years in Aberdeen, 29 in Roxburgh, and 43 in Merioneth. The total number of mice caught in all three areas was precisely 2500.