カヤネズミ

In the breeding season this kind of harvest mouse, Micromys japonicus Thomas, makes a globular nest just like an orange fruit with leaves of wheat (in spring), miscanthus (in late spring to early winter), rice plant (in autumn) etc . at the middle height of their stems (about 0.8 to 1.0 m high) and yields its baby young in it. The author has decided the parturition period, litter size and sex-ratio of this mouse from the result of collection of the nest, suckling and young. This study has chiefly been carried out from May, 1957 to December, 1959 at the dry-river bed of the Chikugo which runs in the suburbs of Kurume City, Fukuoka Prefecture. The results are as follows: 1) The parturition period of this kind of mouse is divided into two periods, namely, May to June and September to December under natural conditions. Among many environmental factors, temperature seems to have a close relation with the parturition period. 2) The average litter size in May to June is 4.00±0.34 (S. E.) (total number of suckling and young are 68 in 17 cases), while 6.11±0.23 (S. E.) (total number 214 in 35 cases) in September to December. As the result of statistical inspection using the confidence of intervals of the population mean (under the level of significance 1 %), significant difference has been found between these two figures. The average litter size throughout a year is 5.42±0.23 (S. E.) (total number 282 in 52 cases). 3) The sex-ratio is ♀100.00 : ♂115.94, but it has been clarified that there is no significant difference between the number of male and female as the result of X^2-test.