Reproductive timing in bats: evidence of spring mating following hibernation

Temperate-zone bats typically mate in autumn, though anecdotal evidence suggests some species may also mate in spring. Using Nyctalus noctula as a model, we investigated post-hibernation reproductive status to assess the occurrence of spring mating. We examined male (buccal glands, testes, epididymides) and female (buccal glands, reproductive cytological status) traits and developed a minimally invasive vaginal lavage method suitable for field-based reproductive assessment in female bats. We found that male epididymides were frequently distended after hibernation, indicating retained sperm despite spermatogenesis being halted during autumn and hibernation. Vaginal cytology showed no evidence of immediate fertilisation after arousal, yet 15% of smears suggested recent mating. Buccal gland size was positively associated with season and epididymis size, consistent with both a sexual and broader social function. Collectively, these findings indicate that active mating in N. noctula can extend into spring, potentially providing opportunities for reproduction before migration. Additionally, we provide the first histological evidence of sperm phagocytosis by neutrophils in bats, supporting the hypothesis of leucocytic clearance of non-viable spermatozoa, as documented in other mammals.