The life history of the Japanese mouse, Mus molossinus Temminck and Schlegel VIII : Habitat of the mouse and its reproduction

The main objects in this survey were to find out whether the Japanese mice, Mus molossinus Temminck and Schlegel, live out in the several environments all the year, and whether they have a breeding season in such different habitats as house, straw stack, cultivated field and waste land. For this reseach the capture of the mice, confirmation of their nest holes, examination on the reproductive status and feeding habit were all carried out in Fukuoka District between June 1955 and April 1960 (Figs. 1-5). The trapping for capture of the mice was all done with break-back traps and cage traps baited with a dumpling made of wheat and buckwheat flours or a piece of cheese. The methods I have used for information on the reproductive status were the examination of implantation scars, corpora lutea, presence or absence of embryos and stage of oestrus cycle as determined by vaginal smears regarding the female, on the other hand, spermatozoa in smears of epididymides regarding the male. The results are shown in Tables 1-8 on the basis of the examination on 929 mice (females 402 ; males 403 ; young and subadults 124) and on nest holes from all kinds of environments : The mice living in the house take groceries as the food, and breed from spring to autumn. But it is clear that very little breeding occurs in winter. In the farm-house, compost and straw stacks adjoining farm-gardens or grass- and weed-grown areas mice were known to have moved from inside to field owing to the feeding. Such the first movement from inside to field occurred in spring, early summer and fall, and the reverse movement was in winter and rainy season. However the mice dwelling in the urban premises are confined to houses all the year. The food of the mice dwelling in the straw stacks is unhulled rice in winter. Straw stacks in this country are built in the end of November after harvest and these are removed by June of the following year. There is, therefore, the breeding season during winter and spring of the following year. At the beginning of winter the mice living in the fields migrate into straw stacks for the winter season. During autumn the mice are found both around straw stacks adjoining the farm-garden and at considerable distances away from farm-garden. The latter probably lives quite independently in the fields. Since the food has been eaten out at the beginning of spring, they moved from straw stacks to the cultivated field. At the end of spring (the rice planting season) mass of the mice in the straw stacks and the other places spread into the dry slopes of hillacks, high banks of paddy fields and farm-gardens. Most mice living in cultivated field live mainly in the farm-garden and marginal banks of paddy fields in summer. They are living on crops, weed seeds and blades. They can live without the shelters such as houses, compost and straw stacks in winter. They live in burrows in the ground at all seasons. Although they seem to have breeding season all the year round, the rates of fecundity in spring and autumn are higher than in the other seasons. The mice living in the waste land live in burrows in the ground under the weed-grown areas and banks, and they are living largely on weed seeds and blades all the year. They seem to have restricted breeding seasons in spring and autumn.著者は1955年6月から1960年4月まで福岡市およびその近郊において環境を異にする9地区11カ所を選び(第1～5図),日本産野棲ハツカネズミの棲息場所とその繁殖について検討してみた.調査の方法としては本種の捕獲,巣孔の確認,食性および生殖状態の吟味などを行なつた.以下その結果を要約してみたい(第1～8表).まず家屋内に棲息している木種は食品を餌として周年ここに棲み,春夏秋によく繁殖している.家屋付近に野菜畑や草場があれば時に採餌のため屋外にでて活動する.一般に藁積は11月下旬につくられ,翌年の5月下旬には取り除かれる.したがつて藁積に棲む本種は初冬から晩春にみられる.藁積では主に籾を餌として冬および春ともに繁殖する.野菜畑を近くにひかえた藁積には本種が多数棲みつき,春には藁積から採餌のため畑にでて活動する.時に本種は野菜畑から遠く離れたところに棲むこともある.耕地では作物が畑に繁茂している間は作物を餌としてここに周年穴居するが,付近に家屋や堆肥,藁積があれば,これに移り棲むことがある.とくに梅雨季,冬季においてこのような現象が観察された.また水田地においては夏は土手に棲む.耕地でも繁殖状態にあるものは周年みられるが,とくに春と秋とに多い.原野に棲む本種は雑草の茎葉,種実を餌として周年土中に穴居または雑草中に棲息する.その繁殖ははつきり春秋に限られる.要するに人間社会から離れた孤立地区に棲息する原始生活型の本種は雑草の茎葉と種実を餌として土中に穴居し,その繁殖現象には春と秋の明瞭な2つの繁殖季節を留めている.これに反し,一般に人間の生活領域に入つてきている本種は餌や棲息場所を人間に依存し,周年にわたつて繁殖可能となり,明確な繁殖季節を認めがたい.このことは環境としての棲息場所が本種の繁殖現象にいかに大きな影響を与えているかを充分に物語るものである