Reproductive asynchrony and its potential role in the mating system of the meadow voles

Ims (1987a) hypothesized that the spatial distribution pattern of male voles may be influenced by the temporal distribution of females. When females enter estrus synchronously (i.e. are clumped in time) they represent a defendable resource and males should defend a territory containing a cluster of females. When females breed asynchronously, males should not be territorial. In this study we examined the role of female breeding synchrony on the spacing strategies of male meadow voles Microtus pennsylvanicus (Ord, 1815). Maternity was determined by the transfer of a unique combination of radionuclides from mother to offspring. The date of conception (to the nearest week) was determined by the weight at first capture of newly recruited voles. The number of litters conceived per week ranged from zero to four. The null hypothesis that the number of litters conceived per week was distributed randomly could not be rejected in 8 of 9 grid-years (4 years on 3 grids). This finding of breeding asynchrony in a vole species with nonterritorial males is consistent with Ims' hypothesis-.