REPRODUCTION IN A WILD POPULATION OF THE KOREAN STRIPED FIELD-MOUSE, APODEMUS-AGRARIUS CHEJUENSIS

A wild population of the Korean striped field mouse, Apodemus agrarius chejuensis, was investigated in the woods of Mt. Halla, Cheju Island, Korea. During the trapping period, from September 1994 to August 1996 , population densities were high in the spring (April) and autumn (Oct ober), and declined in the winter (December to February). Males weighe d over 35 g had descended testes during the breeding seasons, showing active spermatogenesis from March to November. By contrast, from Decem ber to February, spermatogenesis declined. In concerned to oogenesis, females weighed over 30 g captured from March to November had many Gra afian follicles in their ovaries, while those captured from December t o February had many primary and secondary follicles, occasionally with Graafian follicles which were in the atretic process. In the summer, since there were few pregnant females and critical decline was observe d in the number of captured mice, parturition rates might decrease in July to August when the maximum temperature reached approximately 30 d egrees C. Consequently, the seasonal breeding pattern of the investiga ted population of A. a. chejuensis was bimodal with high reproductive activities in the spring and autumn.