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

Abstract

The breeding of this mouse was studied in 3 areas about equally distant on a nearly north-south line about 360 miles long. Mice (altogether 2500) were collected each month for 2 years and the reproductive organs studied. The breeding season lasts from February or March to September or October. During the winter the sp. is represented, so far as [male][male] are concerned, entirely by small, immature specimens less than a year old. These become fecund next spring and die in the autumn or early winter. The majority of the mature [female][female] also die in autumn or early winter. Breeding starts latest in the most southerly of the 3 areas, and continues latest in the most northerly. This has not been explained. There exists a general correlation between the hours of sunshine per month and the breeding condition of the mice. No correlation was found between temp. or rainfall and breeding.