Figure 19. Schematic comparison of the diversity of different daylight domiciles selected by representative cavernicolous and rupicolous species of Chiroptera that roost in caves and rock crevices, respectively: A crevices in sloping inselbergs, Chaerephon ansorgei; B and C crevices in vertical precipices, Chaerephon major and Tadarida fulminans; D horizontal crevices, Tadarida aegyptiaca; E crevices in boulders at ground level, Chaerephon major and Sauromys petrophilus; F free-hanging in dimly illuminated caverns, often near entrance, Rousettus aegyptiacus; G cavities in roof, Myotis tricolor; H in contact, cavities high in ceiling, Miniopterus natalensis; I free-hanging from ceiling in pitch darkness, Rhinolophus spp.; J high roofs and walls, in contact, Macronycteris vittatus; K partially lit and well-ventilated boulder caves and overhangs, Rhinolophus fumigatus and Taphozous perforatus; L free-hanging from low ceiling, hot and humid, Hipposideros caffer. The scale at the bottom presents an index of the trend of ambient lighting within a cave, which underlies important differences between the roosts selected by cavernicolous bats (modified after Verschuren (1957a) and Brosset (1966a) with additions).
Buildings resemble caves in many ways and suitable buildings, usually the roof spaces, are readily exploited by bats (Figure 15). Although colonies of up to 2,000 Chaerephon pumilus have been estimated to occur in the roof of a sugar mill in KwaZulu-Natal, colonies of most house-dwelling bats are generally much smaller, from a few individuals to a few dozen. Information on dealing with unwanted roof-dwelling bats, as well as further details on where and how to locate bat roosting sites and exit holes within the roof space, are provided by Taylor (2000).
Specialised roost sites
Open structures, such as garages and outhouses, thatched game hides, culverts under roads and the eaves of buildings, are frequently used as night roosts (Monadjem et al. 2009). Many cave-dwelling bats carry their insect prey to such night roosts or feeding stations, which provide temporary shelter. These activities of night-roosting bats can often be located by the piles of discarded insect parts below their feeding spots.
Bats may also be found roosting in a variety of other situations. A most interesting example is the use of sunbird and weaver nests as the favoured diurnal roost sites for woolly bats of the genus Kerivoula (Roberts 1951, Oschadleus 2008).
Figure 20. Sandstone hills in the western Limpopo Valley provide daylight roosts for many crevice-roosting bats, such as Sauromys petrophilus (© F. P. D. Cotterill).
Some bats use artificial roosts such as bat houses (Tuttle 1997, Weier et al. 2019b). These may be most effective when used to relocate nuisance bat colonies from human dwellings, or to attract bats as potential biocontrol agents in agricultural monocultures and in ecotourism developments. Establishing such bat populations offers the opportunity to reduce the use of pesticides in controlling insect pests. However, the possible negative consequences of bat houses in natural ecosystems, where common species may be favoured over rare species, remain to be investigated.
BIOGEOGRAPHY
Biogeography is the study of the spatial patterns in the distribution of biodiversity and the causes of those patterns, especially differences in species’ distributions. At this level, species distribution patterns are explained through a combination of historical factors that have governed events of dispersal, speciation and extinction. Such factors include the influence of geological and climatic changes, notably continental drift, glaciation, variations in sea level, and drainage evolution, in combination with macro-ecological factors that determine the availability of ecological resources to species in an assemblage (Morrone 2009).
GEOLOGY
The geology of a continent has a profound influence on the living organisms that have evolved across its landscapes. Local and regional geological controls on the composition of Africa’s bat faunas provide many textbook examples of this relationship. For example, the distributions of rupicolous and cavernicolous species are associated closely with particular formations of granites, sandstones and limestones that have crevices and caves eroded and weathered into these rocks (Figure 19). The geomorphology of the landscape plays an equally significant role, as such caves and crevices tend to be clustered along cliffs and scarps. In recent times, mining activity has influenced bat roost availability, especially in the gold-rich contact zones of the granite-greenstone belts. These artificial cavities are of great significance to many cavernicolous bat species. Numerous mining shafts and adits have been sunk over the past few centuries at many sites in Namibia, central Zimbabwe, South Africa, Zambia and the southern Democratic Republic of the Congo (DRC).
This overview of the formative events that forged the southern portion of the African continent singles out formations and events that bear directly on the composition of the regional bat fauna, especially rock formations that provide daylight roosts for cavernicolous and rupicolous species. Unless specifically referenced, the remainder of this section draws on syntheses of knowledge of the geology of South Africa, Lesotho and Eswatini (McCarthy and Rubidge 2005, Johnson et al. 2006), Namibia (Miller 2008) and Zimbabwe (Stagman 1978). The geology of Angola, the Congo basin, Botswana, Malawi, Mozambique and Zambia awaits deserving synthesis, with relevant knowledge scattered widely through the primary literature and in the less accessible in-house reports of mining companies.
Ancient basement rocks
The very earliest of events that would come to control bat biogeography occurred as long as 3.8 billion years ago when the first continents – known as cratons – started to form on what was then a young planet. Ultimately, two of these, known as the Kaapvaal and Zimbabwe cratons, came to make up a large part of southern Africa. The granite-greenstone terrain that makes up these cratons contains some of the oldest rocks on earth, as can be seen in the Barberton Mountain Land of South Africa.
The granites that characterise so much of Zimbabwe, and also dominate much of the topography and soils of southern Africa, exhibit a spectrum of ages of formation. The majority of the intrusions that ultimately weathered into Zimbabwe’s extensive granitic shield were formed 2,650 million years ago (hereafter Ma). By contrast, the Cape granites are much younger (∼550 Ma). Prolonged weathering and erosion (Twidale and Vidal Romani 2005) has led to the diversity of landforms characteristic of such exposed granites (e.g. in the Matobo Hills of Zimbabwe, Cotterill (2018a)). The rich variety of these granitic landforms has a strong influence on the soils, hydrology, and vegetation of these landscapes (Whitlow 1980, 1982, Moore et al. 2009) (Figure 22).
Figure 21. Aerial view over the granitic shield near its southwest edge in the Matobo Hills, Zimbabwe. Its crevices, caves, and woodlands provide a rich variety of daylight domiciles for roosting bats (Cotterill 2018a, b) (© F. P. D. Cotterill).
Figure