Reproduction in the rusty bat, Pipistrellus rusticus, in the northern Transvaal bushveld, South Africa.

Rusty bats are seasonally monoestrous and give birth to twins during November. Spermatozoa are present in the epididymides from March to August but absent from the testes from April until September. Males thus store spermatozoa in the epididymis for 5 months of the year (April-August). Mating is initiated during April with uterine horns exhibiting a 3-fold increase in sperm volume between April and July samples. It is concluded that ovulation and fertilization occur during the second half of August. Up to 5 conceptuses per female were recorded, but a maximum of only 2 implantations was observed.