Distribution and Reproductive Activity of the Japanese Large Field Mouse, Apodemus speciosus around the Lake Sayama, Saitama Prefecture

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  • 埼玉県狭山湖畔におけるアカネズミApodemus speciosusの分布と繁殖活動
  • サイタマケン サヤマ コハン ニ オケル アカネズミ Apodemus spe

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Abstract

For the purpose of investigating the distribution and reproductive activities of small mammals in the southern part of Saitama Prefecture, trappings of them were carried out around the shore of the lake Sayama(120-160m in altitude) which is located on the border between Saitama Prefecture and Tokyo Metropolis. The surveys were conducted once every month from July 1979 to April 1981 and also in November 1981. The study area was occupied by secondary forests which were dominated by Quercus serrata and Q. acutissima. Two kinds of snap traps, i.e. Easy Trap and Victor Trap were used and 200 traps except for 160 in August 1979 were set each month at nearly the same places in the forests and on the forest edge at about 20m intervals throughout the survey period. The results obtained are summarized as follows: 1. Only the Japanese large field mice, Apodemus speciosus, were collected and they amounted to 249 individuals in total. The trapping success rates were 17.6% in 1979, 1.4% in 1980 and 1.1% in 1981, respectively. 2. The male individuals with the body weight of 30g and more were regarded as adults, and three stages (the first stage-the size of testes was large, but that of seminal vesicles was still small; the second stage-both the testes and seminal vesicles increased in size and became large; the third stage-an increase in the size of the latter exceeded that of the former) were recognized before they attained the sexual maturity. 3. The females with perforated vagina were not found among the individuals less than 25g in the body weight. On the contrary, among the females with the body weight of 25g and over, the vagina-perforated and/or pregnant or lactating individuals were found, and sexually active females increased in number with increased body weights. 4. From both the degree of development in the reproductive organs and the body weight structure according to month, it is inferred that this species has two reproductively active periods (i.e. spring and late summer to autumn) in a year at Sayama area, the southern part of Saitama Prefecture, in accordance with that of the species in lowlands of Japan proper except for the northern part.

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