The masticatory muscles of the Malayan pangolin, Manis javanica, were observed in dissection, and relative positions of the cranium and the mandible were examined under soft-X ray photographs. The M. temporalis was well-developed in the medial area of the zygomatic process of temporal bone. The M. masseter was found to consist of three large well-developed bundles between the zygomatic arch and the mandible. Based on these observations, it is suggested that the thin V-shaped mandible may act as a substantial support in the ventral portion of the oral cavity, and that the M. masseter and M. temporalis may serve to help fix the shape of mouth, when the pangolin uses the specialized tongue for feeding. We demonstrated that the M. digastricus is at least functionally able to depress and open the mandible. In addition, the well-developed M. mylohyoideus may contribute to the control of intraoral pressure during mastication.

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Histochemical studies were made of the masticatory (temporal, masseter and digastric) muscles of the laboratory mouse, Mus musculus, and laboratory rat, Rattus norvegicus, which are omnivorous, the golden hamster, Mesocricetus auratus, which is omnivorous but with a tendency to eat much vegetable matter, and the Japanese field vole, Microtus montebelli, which is herbivorous. It was found that the masticatory muscles were composed almost entirely of fast-twitch fibers. Interspecific differences were found in the oxidative enzyme activity of the masseter muscle in relation to rodent dietary habits. The masseter muscles of the mouse and rat consisted of fast-twitch oxidative glycolytic and fast-twitch glycolytic fibers, thus they appear to have the capacity for powerful, or sudden, and enduring contractions. The masseter muscles of the hamsters were composed only of fast-twitch intermediate fibers, thus giving them the capacity for moderately enduring contractions, whereas the vole masseter muscles consisted only of fast-twitch oxidative fibers, and consequently they appear to have the capacity for particularly enduring contractions.

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Changes in reproductive parameters were analyzed quantitatively in a natural population of the small Japanese field mouse, Apodemus argenteus. Among individuals born in the current year, the lightest female weighed 8 g at sexual maturity and the lightest male weighed 10 g. Irrespective of season, the lightest mice were found only during the phase of population increase. Among mice that had over-wintered, the lightest individuals of each sex to reproduce during the spring population decline weighed 10 g. In years of high population density, the reproductive rates of females, even at their peak during August, was below 10%. In contrast, in low-density years, much higher rates, over 69%, lasted until October during the increase phase. The patterns for males were almost the same as those of females during survey years. According to multivariate analysis, the reproductive rate of males was largely explained by population density (partial correlation, 0.732), whereas the reproductive rate of females was largely explained by the fluctuation phase (0.848). The number of each sex to reproduce increased in proportion to the density of potentially reproductive mice at lower densities, but then decreased at higher densities. The observed maximun number of reproductively active mice was 15 males and 21 females in a one-hectare grid. Temperature appeared not to cause any variation in the breeding season in this population.

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Den site selection and den use by the red fox, Vulpes vulpes, were studied on the Nemuro Peninsula, eastern Hokkaido, Japan. Certain physical variables of 144 fox den sites were compared with those of 236 randomly selected control locations. The red foxes on the Nemuro Peninsula clearly preferred to den on slopes in woodlands near open spaces and streams. The seasonal pattern of den utilization was studied from June 1986 to May 1987. Red foxes used dens mainly during the period from January to June. Since this period coincides with the gestation, parturition and cub rearing periods of the red fox, it was confirmed that the red fox's den was fundamentally a breeding site. Almost all dens were observed each spring from 1986 to 1996 to establish whether they were used for breeding or not, and it was found that the number of fox families was stable during this decade.

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The errors and the sources of errors made while fixing radiotelemetry locations were estimated in two brown bear, Ursus arctos yesoensis, study areas, in the Shiretoko and Oshima regions of Hokkaido. We measured the sampling error and the bias of test transmitters placed at various points in our study areas. The means of our sampling errors were approximately equal to those previously reported by Springer (1979), while the maxima of our sampling errors and the means of our biases were larger than those of Springer's (1979). We also assessed the amount of error in estimating locations based on measuring three bearings. As the sizes of triangles were positively related to the degree of error in estimating their points, we excluded large (>6.25 ha) triangles from the analysis. The maximum values of the 99% confidence intervals for normalized error distances were 321.4 m in the Shiretoko area and 302.3 m in the Oshima area. These values were compared with Lenth's (1981) Andrews estimators calculated from the original data sets of both study areas. The direct method for estimating radiotelemetry error which we used in this study is easy to calculate and proved not to be inferior to Lenth's (1981) method.

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Five species of bats, Myotis nattereri, M. macrodactylus, Miniopterus fuliginosus, Rhinolophus ferrumequinum and R. cornutus were found to forage in the same habitats in southern Kyushu, Japan. M. nattereri fed mainly on Lepidoptera, Coleoptera, Diptera and Araneae, the proportions of each of these in the diet fluctuating seasonally, however, Lepidoptera and Coleoptera, especially, were consumed selectively. Their available prey items ranged in body length from 5-13 mm in length. M. macrodactylus preyed mainly on Diptera, Trichoptera and Lepidoptera, that were larger (7-20 mm) than those eaten by M. nattereri. Small or medium-sized Lepidoptera constituted the bulk of M. fuliginosus' diet in summer. R. ferrumequinum fed chiefly on larger Diptera, Coleoptera and Lepidoptera measuring 8-45 mm in body length, and clearly selected beetles despite these being relatively few in the trap samples. Lepidoptera and Diptera measuring 7-23 mm were important dietary components for R. cornutus, and despite their abundance being relatively low in summer moths were selectively preyed upon. These five bat species selectively hunted particular prey species in addition to taking food opportunistically. Through differences in both foraging-site and in prey selection, they seem to be able to coexist in the same habitat.

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The grassland ecosystem of Mongolia and adjacent areas of Russia and northeastern China is an important component of the natural ecosystems of Eastern Asia. This grassland ecosystem is unique in that it has been utilized for grazing for a long period of time without deterioration. The Mongolian gazelle, Procapra gutturosa, an important species occurring in this ecosystem, used to be abundant and widely distributed, however, populations have decreased in recent decades and the distribution of the species has become greatly reduced. The contraction of its range began in the early years of the 20th century in China, during the 1970s in Russia, where they completely disappeared, and after the 1950s in Mongolia where the majority of the population now remains. The total population has decreased from about 1.5 million heads in the 1940s to 300,000-500,000 at present. In Mongolia, their range spanned about 780,000 km² in the 1950s, but this has contracted to only 170,000 km² at present. Mongolian gazelles inhabit grasslands and eat mainly grasses such as Stipa spp. and Aneurolepidium chinense. During summer they occur in small groups of 20-30 individuals, and in winter usually of 100-120 individuals, although they sometimes gather into herds of several thousands during periods of snow. They migrate seasonally, but their routes and the distances travelled are unclear. Their reproductive capacity is high with very high pregnancy rates ranging from 80% to 100% among females older than 1.5 years. The present problems facing the population and the future needs for conservation are discussed with the main conclusion being that international cooperation for the establishment of reserves is urgently required.

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