As the sun sets over the endless fields of sugarcane, our Swazi field assistant, Mduduzi, parks along the side of the road. We jump out of our van holding a homemade bucket trap and rush to a nearby house. As we approach the house, hundreds of bats come pouring out of an old ventilation shaft. We position our pole-mounted bucket just beneath the emergence hole and are instantly rewarded with the familiar sound of bats dropping into the bucket. We gently lift each chittering bat from the bucket trap and choose an adult female for radiotracking. Before she is released into the night sky, we glue a tiny transmitter to her back. Then we pile back into the van and drive in the direction of the radio signal.
Africa presents a vast frontier for bat research. Here, challenges facing scientists are often daunting, but the rewards in new knowledge are great, since the scientific studies that drive bat conservation are rare throughout most of the continent. The ability of insect-eating bats to reduce damage to farm crops has been demonstrated around the world – but until now, not in Africa.
We were in Swaziland to conduct our Master's degree research studies on the potential benefits of Angolan free-tailed bats (Mops condylurus) and little free-tailed bats (Chaerephon pumila), supported in part by a Bat Conservation International Student Research Scholarship. Working closely with Ara Monadjem from the University of Swaziland and Tom Gilbert from the Centre for GeoGenetics at the Natural History Museum of Denmark, we are able to combine our fieldwork with state-of-the-art DNA analyses and demonstrate the likelihood that these two species eat insect pests over fields of sugarcane.
Sugarcane is a major industry and primary export in Swaziland, and sugarcane fields cover vast stretches of the country. While many animals, especially larger mammals, have declined sharply due to the loss of natural habitats, others seem to survive – and sometimes even thrive – in these human-made habitats, such as the insect-rich fields of sugarcane. Because free-tailed bats are such animals, and their wing and echolocation characteristics are adapted to feeding over open spaces, they are excellent candidates for providing insect pest control over fields of sugarcane.
During our three months of fieldwork, we radiotracked a total of 20 bats, one at a time. Frequent delays were caused by bats rubbing off their transmitters or simply disappearing over the fields. We also got lost in the never-ending maze of sugarcane, became stuck on muddy roads and encountered hissing, venomous puff adders.
In addition to radiotracking the bats to determine where they prefer to forage, our goal was to figure out which insects the bats eat. To do that, we needed to locate roosts where we can collect bat guano for molecular analyses.
Tag along with us to the northeastern part of Swaziland, as we explored the pest-control potential of two free-tailed bat species.
We drive our van slowly through a small Swazi village with our heads poking out of the van's windows. Our eyes are closed, but our noses are hard at work, sniffing the air for the unmistakable odor of the free-tailed bats' roosting sites. After awhile, we smell the bats, jump out of the van and follow the smell on foot. We end up at a house where we spot old bat pellets beneath the bats' entrance hole. The residents greet us warmly – and promptly ask if we can help them get rid of the bats. We decline, but they nonetheless give us permission to place a board covered in "cling film" beneath the roost entrance. We hope that the bats will leave droppings on the board as they fly in and out of the roost. And indeed they do. Before we head back to Copenhagen, we are able to collect guano from several roosts without disturbing the bats.
At the University of Copenhagen, we analyze our radio-tracking data and perform molecular analyses on the feces using DNA barcoding combined with state-of-the-art, next-generation sequencing in order to determine what the bats have been feeding on. To do that, we target mini-barcodes from the insect DNA in the bat pellets, using a short fragment in the so-called barcoding region to identify insect remains.
BCI Scholarship recipient Elizabeth Clare in Canada previously used full barcode sequences to identify insects down to the genus or species of more than three-quarters of the sequences obtained from bat pellets (see BATS, Winter 2009 and Fall 2011). That, however, requires a database of identified DNA sequences for matching. At the time of our study, however, the Barcode of Life Data Systems database included only a small amount of insect-barcodes from Swaziland and South Africa. Due to this limited reference database, our results were limited mostly to insect orders and families rather than species.
Nonetheless, our DNA analyses show that the bats fed on a wide range of insects, including the moth and beetle families to which sugarcane pests belong. And since our radiotracking results revealed that most bats preferred foraging over the vast, open fields of sugarcane, the free-tailed bats certainly were in the right place to have been eating the sugarcane pest insects.
We hope that our findings will provide incentives for maintaining the bats in this and other agricultural areas, for these free-tailed bats face great challenges. Their natural day-roosting sites are narrow crevices in trees and rocks. These natural roosts are declining, but the bats have no problem moving into buildings. Sharing your house with a colony of free-tailed bats, however, can be problematic, since they are smelly, noisy and produce large quantities of guano. Therefore, residents often evict them by blocking the entrance holes at night, while the bats are foraging. One way to help these "homeless" bats could be to provide alternative roosting sites by placing bat houses around the sugarcane fields. This would keep the bats around the fields, where they could be of economic value to the sugarcane industry.
Today, three years after our fieldwork in Swaziland, our study has inspired similar research into bats' pest-control potential in South African macadamia and citrus plantations. The prospects of a growing collaboration between bat biologists and agricultural industries suggest a more promising future for Africa's bats.
CHRISTINA LEHMKUHL NOER received her Master's in biology from the University of Copenhagen and is an education officer at the Natural History Museum of Denmark, University of Copenhagen. KRISTINE BOHMANN is a Ph.D. student at the Centre for GeoGenetics, Natural History Museum of Denmark.
We collaborated on this study with Associate Professor Ara Monadjem of the Department of Biological Sciences, University of Swaziland; Associate Professor Tom Gilbert at the Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen; and Professor Torben Dabelsteen, Behavioural Ecology Department of Biology, University of Copenhagen. In addition to BCI, the research was supported by the Royal Swaziland Sugar Corporation, Etatsraad Georg Bestle og Hustrus Mindelegat, Oticon Fonden and All Out Africa.