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Strange (unfamiliar) males affect survival of progeny of reproductive female rodents in a variety of ways. In mice, strange males block pregnancy before implantation of embryos (Bruce, 1959) but only in females that are not lactating (Bruce and Parkes, 1961). In voles these males can block pregnancy both before and after implantation (Stehn and Richmond, 1975; Marks and Schadler, 1979; Schadler, 1981). Strange males have also been shown to kill nursing pups in lemmings (Mallory and Brooks, 1978) and mice (Labov, 1980 and vom Saal and Howard, 1982).
The present study in pine voles (Microtus pinetorum) examines the effect of strange males on blockage of pregnancy in lactating voles and on survival and growth of nursing pups.