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The demands of hibernation also lead to interruptions of the reproductive process, and the reproductive patterns of bats show some unique features compared with mammals generally (Adams and Pedersen 2000, Crichton and Krutzsch 2000).

Worldwide, the average length of bat gestation varies from 44 days in Pipistrellus pipistrellus to 7 months in Desmodus rotundus, but typically it is around 2 months (Barclay and Harder 2004). Gestation in southern African bats varies from 60 days in Chaerephon pumilus to an effective 7 or 8 months in species with delayed reproduction.

Bats exhibit three patterns of delayed reproduction: sperm storage, delayed implantation, and retarded embryonic development (for reviews, see Racey 1982, Bernard 1989, Happold and Happold 1990a, Bernard and Cumming 1997). These have evolved in species in tropical as well as temperate biomes, which reveals that these adaptations have a tropical origin (Racey 1982).

Sperm storage: After mating occurs in autumn, viable spermatozoa are stored and nourished in the female’s uterus or oviducts throughout the hibernation period. Eggs are only fertilised once the females have ovulated after arousal from hibernation in spring. Most temperate-climate bats use this phenomenon, as do many southern African Vespertilionidae and Rhinolophidae. The burden of sperm storage might be shared or is confined to one of the sexes. In Neoromicia nana (Bernard et al. 1997), Pipistrellus rusticus (van der Merwe and Rautenbach 1990b), Myotis tricolor (Bernard 1982b), and most Rhinolophidae (Bernard 1983, 1989, Cotterill 1989, 1998), viable sperm is stored predominantly in the female reproductive tract, while in Neoromicia capensis (van der Merwe 1994a) and Nycticeinops schlieffeni (van der Merwe and Rautenbach 1990a), sperm is stored in both the male and female tracts. At the other extreme, only Rhinolophus capensis males store sperm (Bernard 1985), and mating, ovulation and fertilisation all occur after winter.

Delayed implantation: Mating, ovulation and fertilisation occur in autumn, but the implantation and subsequent development of the resulting blastocyst (fertilised ovum) is delayed until after hibernation is completed. In southern Africa, Miniopterus natalensis and M. fraterculus exhibit this phenomenon (Bernard 1980, 1994, Bernard et al. 1996), as does Scotophilus dinganii (van der Merwe et al. 2006).

Retarded embryonic development: Normal mammalian fertilisation and implantation occur, but the embryo’s growth is retarded during hibernation and only resumes after hibernation is over. In southern Africa, Hipposideros caffer exhibits this phenomenon (Bernard and Meester 1982), as does Rhinolophus simulator (Cotterill 1989, 1998). In Scotophilus viridis, delayed implantation occurs in combination with retarded development (van der Merwe et al. 1988).

In addition to these patterns of delayed reproduction in hibernating bats, two basic types of ‘normal’ mammalian reproduction – seasonal polyoestry and seasonal monoestry – are common in non-hibernating southern African bats (Happold and Happold 1990a, Bernard and Cumming 1997). An interesting life history has evolved in the polyoestrous molossid Tadarida fulminans, which breeds over the cool, dry season in southern Africa; this is interpreted as a response to predation on insect prey (aerial plankton) at high altitudes (Cotterill and Fergusson 1993, Cotterill 2001b).

Seasonal polyoestry: More than one pregnancy and birth season occurs during the restricted breeding season, for example, Epomophorus wahlbergi, Mops condylurus and Chaerephon pumilus (Happold and Happold 1989a, 1990a). The high-flying molossid Tadarida fulminans is unique among known bats, as females lactate over the cool, dry season (Cotterill and Fergusson 1993).

Seasonal monoestry: Only a single pregnancy and birth season occurs during the restricted summer breeding season (e.g. the majority of bats, including most Vespertilionidae).

Most bats give birth to a single young per litter (Barclay and Harder 2004), while some Vespertilionidae such as Neoromicia nana, N. capensis, Pipistrellus rusticus, Scotophilus species and Nycticeinops schlieffeni commonly give birth to twins or triplets, and sometimes even quadruplets in the case of Neoromicia capensis (see species accounts for details).

Species with widespread distributions may have multiple births in equatorial parts of their range in Africa, but only one or two birth periods in more temperate regions; this seems to be the case in Taphozous mauritianus (Happold and Happold 1990a).

In gregarious species, pregnant females typically form nursery (maternity) colonies in summer. Here, the babies are born, often with the mother clinging upside down to the substrate with her toe claws and one wing claw to maintain a semi-horizontal position. The wing and tail membranes are used to catch the newborn baby. Depending on the species, newborn bats weigh 7–43% of their mother’s weight (compared with 8% in other mammals) (Neuweiler 2000). They have adult-sized hindfeet and deciduous teeth to assist with clinging onto the fur, or pelvic nipples, on the mother’s belly. Babies may be carried for one or two weeks while the mothers forage, but thereafter they are left in nursery clusters. Tadarida brasiliensis mothers at Bracken Caves (Texas, USA) recognise their own young, even though there may be some 4,000 young per square metre (Neuweiler 2000).

In Europe, Pipistrellus species engage in melodious ultrasonic courtship songs to attract females (Park et al. 1996, Russ 2012, Middleton et al. 2014). Male Epomophorus species sing from well-situated calling stations and flash their large fluffs of white shoulder fur to attract mates (Kingdon 1974); they probably also use pheromonal secretions from glands contained in their shoulder pouches.

In some species, it seems that favoured mating territories guarded by certain males are more attractive to females than to the males themselves. In Britain, individual Rhinolophus ferrumequinum guard the same spot at cave entrances over many years (Ransome 1991). The male leks of Hypsignathus monstrosus may represent another example of this (Bradbury 1977).

Bat mating systems exhibit considerable variability. A common pattern is polygyny, in which one dominant male mates with multiple females. This pattern is known in the South American Desmodus rotundus, but may also be common in southern Africa. It appears to be the case in Otomops martiensseni, where a dominant larger-sized male usually challenges approaching intruders with a piercing squeak (P. J. Taylor, M. C. Schoeman, personal observation). Other members of the colony are typically females with juvenile or subadult males and females. In a large cave colony of Coleura afra in Kenya, which exceeded 50,000 individuals, the bats roosted in clusters, the majority of which were harems attended by a single adult male, sometimes with a second ‘satellite male’ on the periphery (McWilliam 1987a). Social monogamy, which is the norm in birds, is rare in bats and has not been shown to occur in any southern African species (McCracken and Wilkinson 2000).

For their size, bats are the slowest-reproducing mammals on Earth (Barclay and Harder 2004). On average, a mother rears only one young per year (Barclay and Harder 2004), and some females are two or three years old before they have their first young (Corbet and Harris 1991). Bats are also incredibly long-lived for their size. Lifespans of 38 years have been recorded (Kritankov and Ovodov 2001), although average longevity is lower at 14.6 years (Tuttle and Stevenson 1982). Mortality is highest in the first year, when some 70% of juveniles may die (Monadjem 2006a, Monadjem et al. 2015). The longevity record for a southern African bat is 13 years for Miniopterus natalensis (van der Merwe 1989). In Eswatini, a banded Nycteris thebaica has lived for at least 10 years (Monadjem et al. 2015).