Bats of Southern and Central Africa. Ara Monadjem
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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).
PREDATION
Although the natural mortality of bats is high in their first year, it is remarkably low in subsequent years of life (Ransome 1995, Bernard and Cumming 1997, Monadjem et al. 2015). In Nycteris thebaica, about 34% of female and 43% of male juveniles survive through the first year, after which survival increases to about 60–70% per year (Monadjem et al. 2015). The survival rates of other southern African bat species are poorly known. Numerous animals hunt bats, including snakes, owls (Cotterill 1992), other birds of prey (Kemp and Rautenbach 1987, Thomsett 1987, Fenton et al. 1994, Fenton 1995), certain passerine birds, small carnivores such as genets and domestic cats, and humans. Some bats, for example Nycteris grandis of Central and southern Africa (Fenton et al. 1993), also eat other bats, while the bat hawk (Macheiramphus alcinus) is a specialised avian predator of bats (Hustler and Dean 2005).
FORAGING ECOLOGY AND ASSOCIATED ECOLOGICAL SERVICES
In southern Africa, all fruit bats have plant-based diets, while all other bats feed on a wide range of insect prey or, exceptionally in the case of Nycteris grandis, vertebrate prey as well (Fenton et al. 1990, 1993).
Frugivory and nectivory: The pteropodids feed on the fruits, leaves, flowers and nectar of a wide range of indigenous trees, often showing preference for the fruits of Ficus (Jacobsen and Du Plessis 1976, Bonaccorso et al. 2014) and Podocarpus. Soft-fleshed cultivated fruits are also favoured, including mangos, guavas, papayas, avocados, litchis, bananas, dates, and even Syringa berries. Bats prefer ripe fruits, and since most commercial fruits are picked under-ripe for shipping, fruit bats generally should pose no significant risk to fruit orchards (Smithers 1983, Fleming et al. 2009). However, there are apparently exceptions to this generalisation – Rousettus aegyptiacus has been shown to cause damage to litchi orchards in South Africa (Jacobsen and du Plessis 1976).
Carnivory: A few bats, including Nycteris grandis, are carnivorous. This species feeds on smaller vertebrates such as fish, frogs, mice, birds, and even other bats (Fenton et al. 1990, 1993). Elsewhere, notably in tropical America, frog-eating bats exploit the mating calls of frogs, while fish-eating bats have a specialised echolocation system to detect fine ripples on the water surface caused by fish, and sharp, hooked hind claws with which they can gaff their prey. In Europe, the greater noctule bat, Nyctalus lasiopterus, a vespertilionid, predates on high-flying migratory songbirds (Popa-Lisseanu et al. 2007, Estok and Siemers 2009). The possibility of large African bats, namely Scotophilus nigrita and Saccolaimus peli, exploiting this abundant, seasonal prey resource awaits investigation.
Insectivory: Some 70% of bat species worldwide eat insects (Jones and Rydell 2004). Depending to varying extents on their body size, jaw construction, wing shape, foraging behaviour, habitat use, and the nature of their echolocation calls, different insectivorous species feed on different groups of insects. Although studying the diet of insectivorous bats requires detailed microscopic or molecular examination of faecal remains, echolocation frequency, body size, and skull and mandible morphology are good predictors of diet (Jacobs 2000, Schoeman and Jacobs 2003, 2011). Strong robust jaws and long canines are indicative of hard-shelled prey, while a weak jaw with poorly developed coronoid processes is indicative of soft-bodied prey such as moths (Freeman 1979, 1981). In general, smaller bats are limited to smaller prey, while larger bats can take a wide size range of prey (Aldridge and Rautenbach 1987, Jacobs and Barclay 2009).
Aerial feeders, such as most Vespertilionidae, Emballonuridae and Molossidae, hunt flying insects exclusively on the wing; they are typically fast fliers and lack manoeuvrability (Aldridge and Rautenbach 1987). Gleaners, such as Hipposideridae and Rhinolophidae, capture stationary prey from branches or the ground and are typically capable of slow, manoeuvrable flight in confined spaces (Aldridge and Rautenbach 1987). Some species, such as Nycteris thebaica, Hipposideros caffer and certain Rhinolophus species, appear capable of both aerial feeding and gleaning. Some of these species are also perch hunters: they hang on a perch and make quick attacks when prey is detected moving past.
To a large extent, the design of the wing and the structure of the echolocation call together determine the prey that can be taken by a bat (Norberg and Rayner 1987, Schoeman and Jacobs 2008, 2011). This relationship is discussed in detail in the section Echolocation.
There is growing evidence that bats play vitally important ecological roles that may also have significant economic benefits, as bats are the major predators of night-flying insects (Jones et al. 2009, Boyles et al. 2011, Kunz et al. 2011, Maas et al. 2013, 2015, Roemer et al. 2019).
Every year, billions of corn earworm moths (Helicoverpa zea), fall armyworms (Spodoptera frugiperda) and other insects migrate in swarms from northern Mexico into Texas at altitudes of up to 3 km above ground. These insect swarms cause massive crop losses across the southern and central United States, costing the country billions of dollars annually (McCracken 1996, Boyles et al. 2011). Recent research using radar, weather balloons and bat detectors has estimated that the 100 million Tadarida brasiliensis bats occupying Bracken Cave and other major caves in central Texas can eat approximately 1,000 tons of insects each night. Even if only 10% of