diet were corn earworm moths (at 250 mg per moth), these bats would eat 340 million pest species moths each night, saving farmers millions of dollars (McCracken 1996, McCracken and Westbrook 2002, Kalko et al. 2008). Studies using bat detectors suspended on helium balloons in the Sengwa Wildlife Research Area, Zimbabwe, also demonstrated feeding by high-flying free-tailed bats (including Otomops martiensseni and Tadarida species) and Taphozous mauritianus at over 500 m above ground (Fenton and Griffin 1997). High-flying bats present unique challenges to conservation planners and managers, because these small mammals suffer impacts of aircraft strikes, pesticides and light pollution (Voigt et al. 2018).
Agricultural pests also featured prominently in the diet of bats occupying the fertile Sacramento Valley (Long et al. 1998). In another study reported in New Scientist magazine (Anonymous 1999), California pear farmers suffered crop losses of less than 5% to the corn earworm when a bat colony was situated within 2 km; when the bat colony was situated over 4 km away, crop losses of 60% were reported.
Closer to home, South Africa’s largest colony of 300,000 bats at the De Hoop Guano Cave assists farmers in the Bredasdorp area by consuming approximately 100 tons of insects annually, including many crop pests (McDonald et al. 1990b). South Africa is the largest exporter of macadamia nuts in the world. Insectivorous bats in macadamia orchards in the Soutpansberg prey on a range of insect pests, including two moths (Thaumatotibia batrachopa, Cryptophlebia peltastica) and two stink bugs (Nezara viridula, Bathycoelia distincta) that cause the greatest damage to this crop (Weier et al. 2019a). Using an avoided cost model based on consumption estimates, bat predation of stink bugs (the most damaging of pests in this industry) reduces total direct and indirect avoided costs to South African macadamia farmers by around US$150 per hectare per annum (Taylor et al. 2018c). However, these values are apparently underestimated: exclusion experiments in macadamia orchards in the Levubu area of Limpopo demonstrated that combined bat and bird exclusion could result in economic losses (due to decreased yield and quality from insect damage) of up to US$5,000 per hectare per annum or 60% of yield (Linden et al. 2019). These studies also demonstrated that by maintaining patches of natural vegetation within and around orchards, farmers were able to benefit from the pest consumption services of bats, whose foraging is concentrated in these patches (Weier et al. 2018). In Eswatini, molossid bats forage preferentially over sugarcane fields (Noer et al. 2012) where they consume a number of pest insects, including the most serious sugarcane pest, Eldana saccharina (Bohmann et al. 2011). Sugarcane fields typically support higher bat activity than neighbouring native savanna, albeit by a lower diversity of species (Mtsetfwa et al. 2018, Shapiro et al. in press).
With a growing emphasis on biological control and integrated pest management to reduce environmental impacts, more and more farmers are taking bats seriously as allies, especially given the evidence that a single colony of bats may consume millions of insects, including crop pests, each growing season. For this reason, farmers throughout southern Africa are now exploring ways of attracting bat colonies to their fields; these include erecting bat houses (Weier et al. 2019b).
Bats may also be important in mosquito control. In a laboratory experiment, bats of the genus Myotis were recorded capturing up to 600 mosquitoes in an hour (Griffin et al. 1960). Mosquitoes have been found in the diet of certain species of bats worldwide, but a priority for research is to establish their importance in the diet of southern African bats.
Fruit bats also bring important ecological and economic benefits. Research sponsored by Bat Conservation International has shown that the seed dispersal and pollination activities of fruit-eating bats are vital to the survival of equatorial and tropical rainforests. Some 300 plant species in the Old World tropics alone depend on bats for pollination or seed dispersal or both, providing more than 450 economically important products valued at hundreds of millions of US dollars annually (Fujita and Tuttle 1991). Seeds dropped by tropical bats are estimated to contribute towards some 95% of forest regrowth on cleared land in the African tropics (www.batcon.org). Certain bat-dependent trees, such as the baobab, Adansonia digitata (whose white flowers may help attract bats at night), are ecologically crucial, supporting dozens of other species. Extinction of baobabs resulting from the extinction of the Epomophorus species that pollinate them would trigger a cascade of linked extinctions. While recent observation anecdotally recorded Epomophorus sp. individuals visiting baobab flowers for nectar in Zimbabwe, efforts involving citizen scientists monitoring flowering baobabs (from dusk to midnight) in the Limpopo Province of South Africa recorded no fruit bat flower visitors during 32 tree-nights of observations (Taylor 2018). A range of insect flower visitors, including moths and beetles, were recorded and these attracted relatively high insectivorous bat activity.
ROOSTING HABITS
Different species of bats roost in various places during the day, such as among foliage, in hollows or crevices, and in specialised roosts, notably caves (Figures 13, 14, 18).
Figure 13. Different views (a, b, c) of one of the bat houses in Letaba Campsite, Kruger National Park. These bat houses provide alternative roosts for molossid bats, which likely control insect populations, including mosquitoes (© F. P. D. Cotterill).
Figure 14. Schematic comparison of the diversity of different daylight domiciles selected by representative species of African Chiroptera that roost in trees: A free-hanging from main boughs, Eidolon helvum; B clinging under exfoliating bark, Laephotis spp., Nycticeinops schlieffeni, and Pipistrellus spp.; C clinging within foliage, reliant on crypsis, Glauconycteris variegata; D clinging within cracks within an elephant-damaged branch, Chaerephon chapini; E clinging in hollow branches, Chaerephon pumilus; F free-hanging in large cavity of tree trunk, Nycteris grandis; G clinging on tree trunk, Taphozous mauritianus; H free-hanging under exposed roots, Nycteris spp.; I sheltering under elephant-stripped bark, Taphozous mauritianus; J deep in dense foliage, Scotoecus spp.; K free-hanging in shrubs, Lavia frons; L inside disused bird nests or spider nests, Kerivoula spp.; M in hollow boles high up in tree, Mops condylurus and M. niveiventer; N under exfoliating bark, Chaerephon nigeriae; O in narrow holes, small-bodied Molossidae (modified after Verschuren (1957a) and Brosset (1966a) with addition of unpublished data, F. P. D. Cotterill).
Foliage-roosting bats
Most Pteropodidae, as well as Taphozous mauritianus, Neoromicia nana, Glauconycteris variegata and Myotis welwitschii, hang up or cling onto surfaces in trees or shrubs. Pteropodidae, G. variegata and M. welwitschii hang by their hind claws from the undersurface of leaves or branches, the last two hanging in a disguised manner among clumps of leaves. Taphozous mauritianus roosts face-down, anchored by its hind claws, but with its belly, thumb claws and hind claws in contact with the surface of a tree or wall. Neoromicia nana clings with its ventral surface in contact with the smooth surface of unfurling banana leaves (Taylor 2000). Crypsis of the pelage is a key adaptation for many foliage-roosting bats, such as Taphozous mauritianus and many species of Glauconycteris, Kerivoula and Myotis. Many of the fruit bats also rely on disruptive colouration, exemplified in the ear spots of Epomophorus species (Fenton 1992, Fenton and Simmons 2015).
Hollow-roosting bats
Hollow-roosting bats