Timing of Major Life Events
The breeding season of northern red-backed voles generally extends from May to August. Females are polyestrous and produce two or three litters during the breeding season. The first litter is produced in late May or early June.
Litter size ranges from four to nine. The average litter size is 5.93. Young northern red-backed voles are unable to regulate their temperature successfully until about 18 days. At this time they are weaned and leave the nest. Young grow little during the winter because of low food supplies. Age of sexual maturity depends to some extent on time of birth. About 20% of females from the first litter breed during the summer of birth. The remaining 80%, and later litters, breed the following May. Martell and Fuller found that the onset of summer breeding was related to the time of snowmelt. A late spring was followed by a low rate of maturation of young-of-the-year females.
In dense populations of northern red-backed voles, sexual maturation of young females may be delayed, or they may migrate to a vacant breeding space.
Northern red-backed voles are mainly nocturnal and crepuscular but are of necessity about during the prolonged arctic daylight season.
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