Reproduction in female Eptesicus regulus (Thomas) (Vespertilionidae), in south-western Australia

The reproductive cycle of female Eptesicus regulus is outlined from histological techniques on museum specimens collected in south-western Australia over the last 15 years. E. regulus is monoestrous and gives birth to a single young in November or December. It copulates in autumn and stores sperm over winter. Ovulation and fertilization is at the end of winter. Both ovaries are functional but pregnancy occurs only in the right horn.