Study of reproduction and the ecological structure of the field vole (Microtus agrestis) in Eastern Fennoscandia

Abstract

Materials (1956–2013) on the reproduction and ecological (sex and age) structure of the field vole (Microtus agrestis) in northwestern Russia are analyzed. It is revealed that the reproduction period of this species within the study region starts in early April and lasts until September. During this time, overwintered and young females give birth to 2–3 broods. Several seasonal generations of young specimens are present in the population of M. agrestis. They differ in the rate of growth and development, as well as in the degree of their participation in reproduction. Yearlings of the early broods are characterized by rapid growth. Almost all of them breed in the year of birth. Most young specimens born in June or later reach maturity only after wintering. The former provide population growth in the current year, while the latter represent the basis of the late summer and autumn population in the next year. A brood consists of 2 to 10, 5.7 ± 0.2, specimens. It is higher to some degree than the corresponding values for specimens from regions located to the south. Embryonic mortality is about 2%. The mortality of cubs in nests is 20%. The intensity and dates of reproduction change by year depending on the ecological conditions and the initial size of populations. The registered age polymorphism promotes stability and functions as a mechanism of population autoregulation.