Both sexes accumulate fat deposits in late summer and autumn, but females begin to do this earlier and accumulate more than males. These deposits are gradually depleted over the course of winter. In autumn females produce a follicle of hibernation, the rupture of which is delayed until spring, when the resultant secondary oocyte is fertilised by sperm stored in the female reproductive tract. Females are monoestrous. Both ovaries are functional, although implantation occurs only in the right uterine horn.
Males also undergo an annual cycle.
Plasma androgen concentration and seminiferous tubule diameter reach a pack in late summer, with subsequent release of spermatozoa, but the accessory sex glands do not reach maximum size until late autumn. Sperm are present in the epididymides of males more than one year of age for the duration of winter. Male V. vulturnus arouse from torpor during winter more frequently than females. It is hypothesised that they do this in order to copulate, even though females store sperm and a copulatory plug forms in the vagina after insemination. Vespadelus regulus and V. darlingtoni appear to have a reproductive cycle similar to that of V. vulturnus .