Reproduction Ecology of the Bank Vole Myodes (Clethrionomys) glareolus Schreb. at the Northern Periphery of the Range: Communication 2. Sexual Maturation and Fertility of Adults and Juveniles

Abstract

Over many years of field studies (1958–2017), we determined that, under the conditions of the northern periphery of the range, the rate of sexual maturation of bank vole juveniles depends on the calendar date of birth more than on the absolute age. It was noted that individuals can reproduce as early as 25–30 days after birth. The earlier the animals are born, the faster they grow and develop and the earlier they mature and begin to reproduce. It was established that males and females born later than June do not generally mature in the year of birth and reproduce only the next spring, after wintering, and although among them there are mature individuals (mainly July broods), their number does not exceed 21%. It was found that the rapidly developing underyearlings of early broods, almost without exception participating in reproduction in the year of birth, provide population growth by the fall of the current year, and those born in the second half of summer serve as a population reserve for the next breeding season. We registered the age-related differences in the quality of the population and a clear “distribution of responsibilities” between individual generations, which are quite labile and serve as one of the most important mechanisms of population regulation. It was also noted that the fertility of adult and breeding new females depends not only on the environmental conditions, but also on their numbers in spring.