Five‐year Surveillance of Small Mammal Abundance in Scandinavian1

Abstract

ABSTRACTA large‐scale surveillance system was established in 1971. It was based on the practical needs for information on the fluctuation in numbers of harmful rodents and the desirability of forecasts. The sampling method used was the Small Quadrat Method (SQM). The annual surveys covered about 50 localities in Norway, Sweden and Finland, the total number of SQ's being over 2,000, and the total number of specimens caught approaching 18,000.In terms of numbers, the dominant rodent species were Microtus agrestis (L.) and Clethrionomys glareolus (Schreber), the former clearly dominating in Finland, the latter in most regions of the other 2 countries. In southern Sweden and Norway, Apodemus species were also relatively abundant, as was Sorex araneus L. in certain regions. During the 5‐year period under study, the numbers of M. agrestis peaked twice (1972 and 1975) in Finland but only once in Sweden and Norway. The peak years of C. glareolus mosdy coincided with those of M. agrestis but, in some areas, were slightly earlier. Fluctuation in numbers of Insectivora did not seem to be correlated with that of the rodents. The usefulness of the SQ indices as a basis of short‐term forecasts is apparent, while criteria for long‐term forecasts require further analysis.