The sun goes down and as the shadows lengthen, small patches of darkness detach from roof eaves and sail towards nearby trees, crisscrossing the sky.
In medieval Europe bats were synonymous with witchcraft and black magic. Later, Bram Stoker’s Dracula cemented into our collective consciousness the image of a crepuscular, blood-sucking fiend.
In West African countries, bats are synonymous with the deadly Ebola virus, which has killed thousands of people, even though only specific bats are carriers rather than all bats.
But without them our agricultural systems would collapse, with disastrous financial consequences, and natural ecosystems would struggle to survive.
“Insect-eating bats, which make up more than 90% of the bat diversity, are the only group that is known to eat night-flying insects,” says Ernest Seamark, director at South Africa-based conservation group AfricanBats. “These insectivore bats can consume about 25% to 50% of their own body mass in insects per night.”
He cites the example of the Natal long-fingered bat, where populations at De Hoop in the Western Cape and Gatkop Cave in Limpopo – estimated to contain about half a million bats – will eat about 4.5 to nine tonnes of insects a year.
Friends of the farmer
This is particularly important for farmers. Not only do bat populations control agricultural pests but also the various pathogens, such as plant fungi, that the pests carry, says Seamark. Research by Peter Taylor, a professor at the University of Venda, found that bats fed on stink bugs in macadamia plantations. These bugs can result in crop losses of up to 80%, according to the department of agriculture, forestry and fisheries.
Fruit bats are also “known for seed dispersal, which leads to forest regeneration”, Seamark says. “Work in South America … has shown that if the fruit passes through the gut of a fruit bat, there is a much higher germination rate than that of the same … fruit passing through the gut of a bird or primate. The bat intestine seems to coat the seeds with a natural fungicide,” he explains.
But bats, the second most diverse mammal group in the world with more than 1 350 species described, are under threat from many quarters, with each continent – and even country – having its own set of bat-related concerns.
Citizens in West African countries had, until recently, relied on bat meat as an important part of their diet, Alexandra Kamins, a research analyst at the Colorado Hospital Association, wrote on Australian academic news site The Conversation.
The United Nations has cautioned people against eating bush and bat meat, following the Ebola outbreak in West Africa. According to the World Health Organisation, about 5 000 people have died from Ebola and more than 13 000 cases have been reported.
“The West African epidemic is thought to have started when the virus crossed over from infected wildlife into the human population and subsequently began spreading between people,” the UN said. “The Ebola virus is transmitted by direct contact with the blood and body of infected people and animals. And fruit bats – usually eaten dried or in a spicy soup – are thought to be the most likely reservoir species for the virus.”
Seamark, who has studied bats for more than 20 years, says that because of the “perceived Ebola threat … [many bats] are being killed or chased out of [their habitats]”.
In the United States, Canada and Europe, the march of green technology is having unintended consequences for bats and their natural ecosystems. New research by the US Geological Survey, published in the journal Proceedings of the National Academy of Sciences, has found that wind turbines are causing “unprecedented numbers of bat fatalities”.
Rather than being killed by wind turbines in windy conditions, the researchers found that bats – specifically tree-roosting bats – were most likely to approach the turbines from below in low-wind conditions.
“Fatalities of tree bats at turbines may be the consequence of behaviours that evolved to provide selective advantage when elicited by tall trees,” the researchers write. But these bats are now “maladapted” to wind turbines because they treat them as though they were trees, rather than something that can kill them.
“Wind energy is a recent technology that has been employed and [the impacts on] bats and birds were never thought of … Can South Africa afford to lose similar numbers?” Seamark asks.
The South African Wind Energy Association told the Mail & Guardian this week that “wind turbines definitely do [have an] impact [on] bats”. This is why an environmental impact assessment must be submitted to the department of environmental affairs (DEA) before a proposed wind farm can be built.
“Part of the process is a year’s worth of bird and bat monitoring on the proposed site: what type of bats are there, what are possible issues, and what is the mitigation strategy. The DEA makes a decision based on that,” it said.
“Through detailed studies and the environmental impact assessment, we hope to mitigate this [negative] impact on bat and bird populations.”
Asked whether wind turbines were a serious concern to tree-roosting bats, Seamark says: “The loss of trees to habitat transformation is still the primary threat to those species that still rely on tree roosts” and have not taken to roosting in houses. He points to pesticides and urbanisation as the major threats to bats in South Africa.
There is very little data about these threats and bat populations. Although North American researchers have had active bat monitoring programmes for more than half a century, and so can comment on their declining bat numbers, “in South Africa, we just don’t have the data to say if our bat numbers are stable, decreasing or increasing, especially at species level”.
However, in light of the Ebola outbreak, many of the fears around bats have returned. Professor Wanda Markotter, a professor at the University of Pretoria who focuses on bat-borne viruses, dismisses the idea that South African bats could carry Ebola. “We do not have the threat of Ebola [from our bats]. Ebola bats are very specific and they do not migrate,” she says.
Although she acknowledges that “there are diseases associated with bats”, to date only two people in South Africa have died from viruses, specifically rabies, they have contracted from bats.
“It’s important that we don’t portray bats as these carriers of diseases. You dog, your cat, your cow: they all carry diseases,” Markotter says.
Asked why bats have developed such a bad reputation, she says that there is “the perception of unknown things flying around at night … that they suck blood. Dracula!”
She chuckles. “We don’t even have vampire bats in South Africa.”