Relations between reproductive conditions and microhabitat use in two woodland rodent species, Apodemus argenteus and A. speciosus, were examined in northern Kyushu, Japan. In both species sexual differences in microhabitat use by sexually active individuals were not significant. Sexually active males of both species and active (estrous) females of A. argenteus selected significantly more favorable microhabitats than did sexually inactive males and females. Microhabitat use by sexually active A. argenteus showed lower heterogeneity than that used by inactive individuals of both sexes, while microhabitat use by A. speciosus indicated high heterogeneity except for sexually active females. Pregnant or nursing female A. speciosus tended to select more heterogeneous microhabitats than did sexually active females. The differences in microhabitat use and its heterogeneity were found to depend on reproductive condition in both species.

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The age at puberty, pregnancy rate and the occurrence of accessory corpora lutea (ACL) were investigated in female sika deer killed between late February and mid-March in Hyogo Prefecture. No fawns had ovulated but puberty occurred in most of yearlings. The pregnancy rate of yearlings and of older females was calculated to be over 90%. These show that the population has high reproductive performance. ACL were found in 80.7% of 57 animals that had ovulated, and females with ACL carried heavier fetuses than those without ACL.

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The grey red-backed vole Clethrionomys rufocanus bedfordiae shows cyclic fluctuations in its population density. Although one possible factor involved is thought to be relatedness among individuals, its effects on population fluctuations still remain unknown due to the lack of a precise method for paternity identification. In seeking a means to establish paternity, the availability of DNA fingerprinting was examined with a human minisatellite DNA probe in the members of six vole families established from laboratory bred wild born parents. The probe was able to detect individual specific band patterns on vole DNA digested with restriction enzymes recognizing four basepair cleavage sites. The parentage of each family was unequivocally established by comparing DNA fingerprints between each offspring and the parents after digestion of DNA with HaeIII, or AluI, or both. Therefore, DNA fingerprinting analysis may allow precise paternity identification in the grey redbacked vole.

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The growth, sexual dimorphism, and geographical variation in skulls of 596 brown bears (Ursus arctos) hunted in Hokkaido, Japan from 1971 to 1986 were investigated. Most cranial traits continued to increase after the age of sexual maturity, and in particular skulls became progressively wider with age. Skulls of males, even those of cubs and yearlings, were larger than those of females, and the difference became significant after two years of age. Skull dimensions tended to increase from south to north, in Hokkaido, and bears from the north-eastern region possessed higher brain cases and longer mandibles relative to skull length and width, than those in the southern region.

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