Cave-dwelling is not much in vogue these days, but it was probably through sharing caves that humans and bats first had a close association. For most people, the idea of living in a cave brings to mind images of pre-historic cave dwellers or Fred Flintstone in the TV cartoon series. But in some parts of the world, caves have offered shelter for certain communities right up to the present day. One such place is Mt Elgon, an extinct volcano on the Kenya Uganda border, where within living memory some of the famous elephant-caves were used as spacious homes by local people, with different areas cordoned off inside for their cattle and goats. The walls of these caves are blackened by generations of cooking fires, but behind the soot you can often see hundreds of smooth furrows forming a random pattern; these are tuskings, formed by salt-hungry elephants gauging the mineral-rich rock with the tips of their tusks. The people, and the bats, of Elgon were living in former elephant salt-mines. Resident humans are now a thing of the past (apart from the occasional field biologist) but the caves remain the focus of activity for much of the area’s wildlife. The best known of these caves – Kitum and Mackingeni - are open to visitors in the Mount Elgon National Park, Kenya and what better time to visit than the Year of the Bat.
Look up as you enter and you’ll see that the soot-blackened surface is gradually being eroded away in places by the claws of roosting bats in the ceiling, and the resumed tusking of the cave walls by elephants. In side chambers, excavated by people in the past to feed the mineral-rich rock to their livestock, the ceiling is dotted here and there by solitary-roosting Rhinolophus horseshoe bats. Occasionally you’ll come across a colony of Miniopterus that pack together so tightly they look like a mat of bat stuck to the roof. Roof-falls have created higher parts of the ceiling in the cavernous entrance chamber of Mackingeni, and in the inner recesses of Kitum, and there you’ll hear the rising squeals and chatter of large roosts of Rousette’s Tongue-clicking Fruit Bats (Rousettus spp.) On the guano-spattered rocks beneath crawl blood-sucking insects, trying to find their way back up to the bats. These are Afrocimex and bear a strong resemblance to the human bed bug Cimex – perhaps an evolutionary indication of humans and bats cohabiting before we moved on to building our own ‘caves’ out of bricks and mortar.
Unlike insectivorous bats, fruit bats navigate by sight and have large eyes, so looking up along the beam of your flashlight reveals a moving constellation of thousands of bats’ eyes reflecting back the light. Most species of fruit bat roost in trees, but Rousette’s Bats roost in the dark zone of caves – which you might think would present a problem for visually orientating bats. If the bats take fright at your torchlight, however, you will hear the eponymous clicking of tongues – tut, tut, tut – because these bats navigate using a rudimentary sonar, gaining an understanding of the cave topography from the echoes of each tut. It is nothing like as sophisticated as that of the smaller insectivorous bats, who can turn and wheel in the air to catch flying insects, but to be fair, fruit bats have less agile food and just need to find a place to hang. In the past, their nightly forays would have been to find fruit trees forests that stretched as far as a bat could fly. Unfortunately, pressure for farmland in this fertile part of Kenya now means that all the lower slopes outside the park are intensively cultivated and the bats forage in farmland – making them a nuisance for fruit growers.
Bats hang by their toe-nails – or toe-claws to be more precise – all five of which curve the same way like a permanently hooked five-pronged rake. If you climb to the roost and take a closer look, you will see how these claws have eroded away the soft volcanic agglomerate leaving an amazing sight: perfectly preserved fossil twigs and branches. Mount Elgon was active in the late Miocene, and volcanic eruptions of ash and pyroclastic materials flattened and covered the forests that grew on its flanks between eruptions. Thanks to the mega-erosion of mining elephants and the mini-erosion of bat claws, the Tongue-clicking fruit bats of Mount Elgon today roost on the fossil branches of petrified trees deep in the dark zone of an elephant salt-mine!
© Ian Redmond
Miniopterus insectivorous bats roost together in cave roof, Mt Elgon NP, Kenya.
© Ian Redmond
Rousettus Tongue-clicking Fruit Bats roost in cave roof, eyes reflect flash, Mt Elgon NP, Kenya.
© Ian Redmond
Soot-blackened cave roof and cattle stockade still in use in 1980s, Kol Cave, Mt Elgon, Kenya.
Epomophorus wahlbergi © Dawn Toussaint
© Gerhard du Preez
It’s the greatest concentration of mammals in Africa but, despite the spectacle of the annual gathering of millions of Straw-coloured Fruit Bats (Eidolon helvum) in the Kasanka National Park in Zambia, it is still considered one of the continent’s best kept secrets. Approximately 8 million of these large, fruit-eating bats gather in the evergreen mashitu swamp forest from late October to mid-December to feast on the fruit of the Red Milkwood (Mimusops caffra), Water Berry (Syzygium cordatum) and Wild Loquat (Uapaca kirkiana) trees every year. Each night, as the sun begins to set, the bats, with 1 meter wide wingspans, fill the skies as they set off on their nightly foraging sessions. Researchers believe that each animal can consume up to twice its own body weight a night, accounting for a mind-boggling 5.000 tonnes of fruit every night.
The enigma that caught the attention of researchers Heidi Richter and Graeme Cumming, among others, was that nobody was certain where the bats came from or where they went to after leaving Kasanka National Park. To answer their questions they fitted light-weight satellite transmitters to the backs of four male bats to track their movements once they left Kasanka. What they found was astounding. The four tagged bats moved up to 2000km from the Kasanka National Park towards the central and northern Democratic Republic of the Congo (DRC) but each animal to another region. Richter and Cumming concluded that the Kasanka colony was composed of individuals drawn from a large area of Central Africa which only came together for those few months to take advantage of the seasonal fruit abundance.
© Dawn Toussaint
© Trevor Morgan
© Trevor Morgan
Some of the many bat species found in Africa
Fruit bats play an important role as pollinators of flowering plants, the dispersal and germination of seed and the subsequent establishment of woody vegetation. The Kasanka bats are thought to be particularly important in this regard as the length, duration and direction of their annual movements suggests that they may disperse seeds and nutrients very widely. This has the potential to affect the long-term sustainability of, not only, Central Africa’s forests but also human livelihoods in an area where most people are still dependent on wood, fruit and other forest products. Conservation of the Straw-coloured Fruit Bat is, thus, vital and the Kasanka Trust, responsible for managing the Kasanka National Park, has recognised this and has implemented on-going research and conservation actions on the bat’s behalf. International cooperation, to protect a functional network of roosting and foraging sites throughout their entire migration routes, in needed to ensure fruit-producing woodlands in northern Zambia and the DRC are maintained for generations to come.
News article on the First BCI Summit on African Bat Conservation
Bracken Bat Cave and Caves and Karsts Webcasts by BatsLIVE