On the collecting and rearing methods of the Japanese harvest mouse, Micromys japonicus Thomas

In this paper, some informations on the collecting and rearing methods of the Japanese harvest mouse, Micromys japonicus Thomas, are described, which have been derived from the author\u27s experiences. The collecting method by means of cage (live) trap gives a high rate of captures in the seasons during late autumn to spring, but in other seasons (summer and autumn) does not so. The author surmises the reason as follows: the artificial baits may not be so attractive in the latter seasons, when there is a plenty of natural foods such as seeds of grasses, fruits and insects, as in the former seasons that bring about the shortage of natural foods. The bait used in the live trap collection was mostly made of one part of wheat flour and one part of buckwheat flour. Fortunately, many suckling young can be easily obtained from the globular nests of these mice in the seasons of summer and autumn (Plate 12, Fig. 1). The author thought out two methods of nursing them and succeeded in them. One way is with the help of nursing mouse of different kind, Mus musculus var. albinus and the other is by means of completely artificial nursing. In the former way, the collected suckling young of the Japanese harvest mouse were previously spread with cow\u27s milk and placed under the care of the nurses that had their own young spread with milk similarly. The suckling young (after the age of 10 days) showed that they could be fed on cow\u27s milk and bread. The young at the age of 12 to 13 days begin to eat solid foods for themselvs such as wheat, seed of barnyard grass and millet (Plate 10, Fig. 2). Beyond this age, to rear them becomes easier. The boxes for rearing the mice have the size of 60×30×30 cm and wire-netting at their two sides (Plate 12, Figs. 3-5). In each of these boxes, a branch of wood was fixed with a straw-made nest for small birds such as lovebirds. Other boxes of the same size supplied with only straws in stead of bird\u27s nest or of different size were used, but no different result was obtained. For parturition of pregnant mice, some wire-netting cages with the size of 20×10×10 cm were used as their maternity wards. Each of these cages had a shelter of small box with the size of 8×6×6 cm. The solid foods daily supplied to this kind of mouse were mainly consisted of five kinds of corns such as unpolished rice, wheat, millet, seeds of barnyard grass and cracked Indian corn. Besides them, dried small sardines, green vegetables (Chinese cabbage, cabbage, sweet potato, pumpkin, cucumber and leaf of raddish), seeds (peanut, nut, pumpkin, foxtail, barnyard grass and millet), fruits (fig, peach, persimmon, strawberry and melon) and insects (grasshoppers etc.) were occasionally supplied to the mice. Fresh water had to be given everyday, too. The quantity of solid foods eaten everyday by this kind of mouse was equal to 25 to 35% of its body weight. The orders of liking of the above mentioned five kinds of corns, shown by the tested mice, were as follows : unpolished rice > cracked Indian corn ≒ wheat > seed of barnyard grass ≒ millet. The longest record of life span of this mouse was 944 days and the next 802 days by means of the above mentioned collecting and rearing methods.此の報告ではカヤネズミの採集・飼育法について,これまでに著者が得た幾つかの知見を述べた.カゴわなによる採集方法は晩秋から春に用いると効率が高いが,夏・秋の候には低い.しかし,後者の候には乳仔が多数採集できるので,それらを飼育することを考えた.飼育法としてヨウシュハツカネズミ雌(白変型)を乳母としてこれに抱かせる方法,乳母ネズミを使わないで人工的に飼育する方法を応用し,両者とも成功した.ことに生後日令12,13日のものは独力で摂餌を始めるので飼育容易である,飼育箱としては60×30×30cmの大きさの木箱に金網を張り,樹の枝,小鳥飼育用のわら巣を取り付けたもの,わらのみを入れ与えたものなどを使用した.また出産用には20×10×10cmの金網張りのカゴを用いた.飼料としては従来の幾つかの報告を参考に,玄米,小麦,アワ,ヒエ,ひき割りトウモロコシを主に給した.その他煮干, 野菜(葉菜,根菜,果菜),種子,果実,野草の種子,昆虫(バッタ類)を与えた.水も毎日新鮮なものを給する必要がある.カヤネズミ1頭あたりの1日摂食量を調べた結果,ほぼ体重の25～35%にあたる量を食することを知つた.玄米,小麦,アワ,ヒエ,ひき割りトウモロコシの5種穀類の嗜好度順位は,玄米＞ひき割りトウモロコシ≒小麦＞ヒエ≒ アワとなる.上述の飼育法で飼育したカヤネズミの最長命個体は944日(雌),つぎは802日(雌)生存した