Given a choice between tea and coffee, bats in the Western Ghats prefer plantations that grow the latter, new research that ought to warm the cockles of kapi-drinking South Indians shows. But beyond a seemingly batty beverage choice is a crucial indicator of habitat preferences and future conservation strategies of a species that is a natural pest controller and good indicator of the health of an ecosystem.
“Bats are the best pest controllers in nature, controlling a large number of insect pests on our agriculture and horticulture produce, while simultaneously working as efficient pollinators and seed dispersers in natural systems,” said bat enthusiast and researcher Rahul Prabhukhanolkar, from the Indian Bat Conservation and Research Unit (BCRU) in Dharwad. They are also important ‘forest planters’, pollinating several plants such as silk cotton, durian and the tequila agave, and dispersing seeds across long distances in forests.
The lure of coffee
A team from the University of Leeds, UK, the National Centre for Biological Sciences (NCBS), Bengaluru, and the Nature Conservation Foundation, Mysore, delved into tea and coffee plantations in India’s Western Ghats, a global biodiversity hotspot. The study area was the Valparai plateau in southern Western Ghats, which was cleared for plantations between 1900 and 1940. About 68% of Valparai is now planted with tea.
Their study, published in the August 2015 issue of the journal Biological Conservation, shows that bats respond negatively to tea plantations that are extensively modified by humans. But they do quite well in shaded coffee plantations and forest patches.
Clair Wordley, a biologist at Leeds University and lead author of the study, told The Wire that traditional coffee growing in India, with native coffee varieties that support bats growth, are giving way to uniform plantations of Coffea robusta that is more popular for the instant coffee market. “Keeping coffee grown in the traditional way with lots of different native trees is great for bat conservation – and they’ll probably thank you by eating some of those insect pests,” she said.
Ecosystem health indicators
Bats are good indicators of the health of an ecosystem, “so if we see them decline, there are probably less of other animals too,” said Wordley. Studies by the Nature Conservation Foundation have shown fewer bird and frog species in tea plantations, “so we can see the whole ecosystem is being affected by the changes in habitat.” About two-thirds of bats eat insects, and are natural pest controllers in cotton fields, rice paddies and coffee plantations, according to her.
“In fact, bats are estimated to save farmers in the United states about $23 billion dollars a year by eating crop pests – imagine what they save farmers globally!”
Bats eat night-flying insects that would not be picked up by day-flying birds, and so have a unique role to play in insect control. Many species are known to eat mosquitoes and other disease carrying insects we well. Prabhukhanolkar cited the example of an insectivore bat that can devour 600-1,000 mosquito-sized insects in one night.
According to him, there is a “dearth of similar studies” on different diverse landscapes in the country, which still identify most of the fruit bats as vermin and provide no protection to insectivores bats under India’s Wildlife Protection Act 1972.
Plantations v. biodiversity
Coffee is traditionally grown under native shade in many areas, including the Western Ghats. The C. arabica coffee is slow to ripen, so is low in yield but high in flavour. As there is more and more demand for cheap coffee, there has been a global shift to planting C. robusta coffee, a tougher breed which grows in full sun, yields more coffee berries but has a less full flavour.
Sadly, this comes at a huge cost to biodiversity. India is one of the countries with the most coffee left under traditional native shade trees, a matter of pride, Wordley exclaimed. “In some coffee growing regions of India such as Kogadu, nearly 100 native tree species can be found on smallholder coffee farms.” And India itself has some 20 bat species.
“But sadly there is still a trend towards robusta coffee in India, with only about 30% of coffee being of the arabica strain; and some arabica planters are moving more towards using commercial, foreign tree species such as eucalyptus for shade, which do not provide a good habitat for many species,” said Wordley.
A depletion in the bat diversity and populations would severely impact agricultural production, cautioned Prabhukhanolkar. There could be insect pest outbreaks in a few areas, less efficient forest regeneration, and an imbalance in the ecosystem services.
Scientists still know very little about the current status of bats in the Western Ghats, whose populations are declining. This is despite the importance of these mountains for biodiversity in general, and the fact that over 50 bat species live there — including one that lives nowhere else.
“We all know that bat populations and diversity in the Western Ghats are under threats from deforestation, forest fragmentation, mono-culture plantations, excess use of insecticides-pesticides, and mining projects,” Prabhukhanolkar remarked.
The study team found fewer bats foraging in tea plantations and struggling to survive there than in small patches of forest or in shade coffee plantations — indicating that many bat species have declined steeply as the forest has been converted to agriculture.
Though scientists still do not know the exact numbers of bats lost, they are encouraged by the fact that many bats are surviving in intensively-farmed lands, thanks to the forest patches, from 2-40 hectares, left by farmers, and traditional coffee-growing in the region. “Even the smallest patches housed some of the most vulnerable bat species. Strips of forest left along river banks were particularly good for bats, as many species like to feed on the insects over the water.”
The study shows that in spite of the continuous accelerated land transformation at landscape level in the Western Ghats, there are hopeful signs that few remaining forest fragments together with mixed agriculture plantation areas are supporting biodiversity.
The caveat is that “if the patches of forest and coffee were lost, we’d lose most of the bats in the area we studied, but a lot more work is needed in different landscapes to be sure of that,” cautioned Wordley.
Also, the researchers found two bat species — the lesser woolly horseshoe bat and the lesser false vampire bat — which never went into tea plantations, and several other species that only foraged for insects within a few hundred metres of forest or coffee patches. “This may mean that less insects are being eaten out in tea plantations — it’s something we need to study further.”
The researchers suggest that since riparian areas are important for bat populations, conservationists could grow trees along river banks to provide shade for bats species.
They also advise that in ecologically sensitive areas such as the Western Ghats, it would be beneficial for biodiversity to prevent further conversion of forest land to tea plantations. Existing tea plantations could have native trees instead of silver oak for shade.
Prabhukhanolkar says the study “will help us in effective planning and sound management of wildlife (bat) friendly plantations. These include shade-grown coffee plantations, in which arabica coffee is grown under a canopy of native tree species supporting bat communities, as rich as forest patches and serving as refuges for biodiversity in the landscape in the region.
The study will also help in understanding important forest fragments at key locations necessary for the wildlife movement and conservation. “Strategically, protecting these priority sites will help in conservation of bat diversity and sustained ecosystem services,” he says.