延岡市サギ島における鼠禍 : I. 基礎調査及び異常増殖に対する考察

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  • Damages of agricultural products caused by the Norway rat in Sagi-shima, a delta of Nobeoka City, Miyazaki Prefecture : I. Preliminary surveys a n d considerationson the cause of rat outbreaks

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In accompany with the stability of the ecosystem, animal populations become to keep balance in a restricted area. When the stability is broken for some reasons, however, the remarkable increasing in number of a certain animal may occur. The rodent outbreaks have frequently repeated and done great damages to human society. Considering on many cases the authors, as many other investigators, have to support the view that rat plagues are intimately accompanied with the increase of the environmental capacity, though Dr. R. Tanaka hardly accept such view. Because of the persistent and contagious plague of the rat in the coastal region of Uwajima, south-west of Shikoku, he concluded that this phenomenon could not be directly attributed to any of the environmental factors. In 1957, the damages of agricultural products caused by the Norway rat, Rattus norvegicus (Berkenhout) was noticed in Sagi-shima, a delta of Nobeoka City, Miyazaki Prefecture, situated on the eastern part of Kyushu, facing the coastal region of Uwajima on the opposite side of the Bungo Channel. Sagishima is an uninhabited and typical delta on the mouth of three large rivers, and has an area of about 100 hectares including cultivated land of about 60 ha (Text-fig. 1). Farmers go to the delta to cultivate by means of small boats across the rivers. We made preliminary surveys to get an effectual device for controlling rats, from February 17 to 21, 1958 in this delta. 1) The cause of the outbreak in Sagi-shima is explained as follows : The Norway rats had been carried to the delta from Nobeoka City by flood which occurred once in a few years ; thereafter they bred gradually with the increase of favorable environmental conditions, such as rich supply of food, diminution of the natural enemies, existence of the suitable habitats and mild climate. Though the delta had been covered by mulberry field before the Second War, the mulberry was taken place by the sweet potato, wheat and upland rice etc. on account of emergency food supply during the War, and after the War cultivation turned to normal. In addition to this, the area of the cultivated land have spread year after year. Therefore the food of the rats became rich. The Japanese weasels and snakes had formerly inhabited in the delta, but they almost disappeared as a result of capture. Grass-grown foot path, drain, waste, bamboo grove, tea tree bush and stone-fence etc. offer the suitable shelters for rats (Figs. 1 and 2). 2) The damage was given to all kinds of the crops such as wheat, sweet potato, upland rice, potato, watermelon and pulse (Figs. 3-8). Especially, the peripheral parts of the field near shelter of the rats were remarkably damaged. 3) The population density was estimated to be about 32 per hectare ( Table 1 and Text-figs. 2 and 3). Judging from the fact that the Norway rat is about ten times heavier than the mouse or vole in body weight, it was natural that considerable damage to the crops was taken place in spite of relatively low density. 4) According to the examination of the feeding habits by the contents of stomachs, percentages of both the average volume and frequency are very high in sweet potato and wheat (Table 2). It was proved that the Norway rats had food reserves during winter because the sweet potatoes were found stored in their burrows under foot path (Fig. 9). 5) The inhabiting rats were in u n usually good nutrition. Addition to this, we recognized that the rats were just before the breeding season judging from the inspection of their genital organs. Therefore, we have to make the plan immediately to control rats ; otherwise the rats will increase by geometrical progression and give us much more severe damage.

生物個体群が平衡状態を保つているのは,その生態系が安定しているからである.種々の要因は複雑にからみあつて個体群に作用する.なんらかの原因によつて生態系の均衡が失われると異常増殖がおこる.今までに鼠禍は幾度となく繰りかえされ,人類に大害をもたらしてきた.加害鼠としてはハタネズミ亜科Microtinaeに属するものが圧倒的に多いが,わが国ではネズミ亜科Murinaeのドブネズミの異常増殖も著しい.昭和33年(1958)1月中旬,宮崎大学中島茂教授はサギ島の鼠禍をわれわれに通知され,同時に捕獲されたドブネズミRattus norvegicus(Berkenhout)を示された.そこで,われわれは2月17日から21日にわたつて鼠禍の原因,被害状況,棲息数,食性および繁殖について基礎調査を行つた.本調査の目的はこれによつて有効な駆除対策を速やかに確立し,一刻も早く鼠禍を終焉させるにあつた.今ここに基礎調査の所見を報告するとともに,従来報告されたドブネズミの異常増殖,特にその原因について考察を試みたい.本文を草するにあたり,同島の鼠禍について最初の知らせを頂いた中島茂教授,調査に同行され協力された帯広営林局合田昌義技官,また種々便宜と援助を賜わつた岡富農業協同組合佐藤改司組合長,河野岩美元参事,山之内峻技師および現地の多くの方々に厚く御礼申し上げる.

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詳細情報 詳細情報について

  • CRID
    1390009224837514752
  • NII論文ID
    110001643427
  • NII書誌ID
    AN0005519X
  • DOI
    10.15017/21505
  • HANDLE
    2324/21505
  • 本文言語コード
    ja
  • データソース種別
    • JaLC
    • IRDB
    • CiNii Articles

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