This study was carried out to clarify the developmental biology of Hokkaido brown bears Ursus arctos yesoensis from birth to approximately 90-day-old. Though the birth date of 107 litters ranged from 11 January to 1 March, 91% of the cubs were born between 17 January and 5 February. The body weight of 40 neonates was 419±40 g (mean±SE) and did not differ significantly between the sexes (p>0.05). Mean litter size was 1.82±0.70 (SE). Mean body weight gain per day, an indicator of bear development, was calculated for 192 cubs from the date and body weight at birth and at about 90-day-old. The body weight gain varied greatly among individuals (range: 0.018-0.130 kg/day) and tended to be smaller as litter size increased. The body weight gain differed significantly (p<0.01) between the sexes when there was only one cub, but not when there were two or more cubs. The mean intake of calories per unit body weight gain from birth to 68 days after birth, was calculated at 4,000 kcal/kg for the hand-reared cubs.

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The reproductive traits of captive Japanese hares Lepus brachyurus (15 female and 12 male) were studied in central Honshu, Japan. The breeding season was from early January to late October during which time the average number of litters was 4.6 (range of 4-5). Litter size ranged from one to four with an average of 1.6. The sex ratio at birth did not differ from 1:1. The average productivity (litters per year × litter size) was estimated to be 7.4 young per female annually. The gestation period averaged 43.9 days (range of 43-45). The interbirth interval was shorter than the gestation period, which indicated the occurrence of superfoetation.

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Daily activity rhythms of three sympatric soricine shrews in Hokkaido were investigated. Nineteen Sorex unguiculatus, 13 S. caecutiens, and 11 S. gracillimus were captured, and their total activities were studied using an infrared sensor system under two different laboratory regimes (16L8D, 20°C and 10L14D, 5-15°C). All the three shrew species were more active during periods of darkness than during light periods; however, during the light periods most of S. gracillimus and some of S. unguiculatus and S. caecutiens exhibited short intermittent activity. Activity during periods of darkness was polymodal for all the three species under the 10L14D, 5-15°C regime, but was bimodal in S. unguiculatus under the 16L8D, 20°C regime. The actogram pattern of S. caecutiens proved to be intermediate between S. unguiculatus and S. gracillimus. Interspecific differences in activity pattern seem to be related to body size in the genus Sorex.

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Adult Formosan squirrels Callosciurus erythraeus thaiwanensis from Ken-ting (Pin-tong Prefecture, Taiwan R. O. C.) were found to be heavier than those introduced in Kamakura (Kanagawa Prefecture, Japan) and Izu-oshima (Tokyo, Japan). Growth rates in the two Japanese populations, estimated by a capture-mark-recapture method under field conditions, were lower than in squirrels reared in cages with a plentiful food supply. Mature body weights, estimated from the regression lines of size-specific growth rates, were much heavier in captivity than in the wild. It is suggested that food availability in the habitats of the two Japanese populations affects growth rates and leads to a smaller body size at maturity than in captive squirrels.

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Multivariate analysis of the mandibular morphometric variation of seven mouse samples revealed that: mice from localities in Aichi Prefecture were Japanese wild mice, as were those on the island of Sakushima whearas those on the island of Himakajima differed both from those of Sakushima and from mainland mice. Mice from Chichijima, the Ogasawara Islands, 1,000 km south of mainland Tokyo, differed greatly from those in Aichi. Himakajima and Sakushima lie a mere 2-5 km from the nearest mainland, and mice are likely to have reached the islands easily. The morphometric heterogeneity between the Himakajima and Sakushima populations is likely to result from there having been different origins for the original colonizers. In contrast, oceanic Chichijima was not inhabited until the 19th century. The mice there have not been clearly identified taxonomically, but they seem to be derived from both the Japanese wild mouse and the European house mouse as a result of a double introduction with the immigration of different peoples to Chichijima.

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Body fat deposition for wintering was examined in two populations of the Norway rat, Rattus norvegicus. Rats on an artificial islet in Tokyo Bay depleted body fat during winter, but maintained body fat throughout the year at an average fat index level (FI) of 0.10±0.04. Non-wintering rats maintained their FIs at higher levels than wintering rats by an average of 0.16±0.06 until December (t-test, p<0.01). Wintering and non-wintering rats on a forested island maintained average FIs of 0.11±0.06 and 0.12±0.06, respectively, with no significant differences between them (p>0.50). There is circumstantial evidence that the Norway rat uses body fat for wintering.

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