Rainforests are being cleared at a frightful rate by loggers, farmers and ranchers, with troubling impacts on biodiversity and climate change. Bats, premier seed-dispersers of the Neotropics, often play a vital role in restoring these battered forests – and now a German biologist is demonstrating that artificial roosts can attract bats to areas where they’re most needed.
Reforestation is becoming an increasing urgent issue, and some areas are being replanted although large-scale tree planting is prohibitively expensive. Natural regeneration, meanwhile, is often hampered by a lack of seed dispersal in cleared forests. Seed-dispersing bats, as well as birds, have little reason to enter open areas, such as abandoned pastures, because they offer little food, shelter or cover.
Detlev Kelm, now of the Leibniz Institute for Zoo and Wildlife Research in Berlin, concluded that fruit bats may avoid cleared areas largely because they lack suitable day roosts – mostly large hollows and crevices in old trees, which are prime targets of loggers.
With partial funding from a Bat Conservation International research scholarships, Kelm worked with Kerstin Wiesner and Otto von Helversen of the University of Erlangen (Germany) to determine whether fruit-eating bats can be attracted into deforested areas in Costa Rica by installing artificial bat roosts, and whether that would increase seed dispersal.
The artificial roosts were designed to mimic the characteristics of the large, hollow tree trunks favored by fruit-feeding bat species in lowland rainforests. They were simple boxes, about 6.5 feet (2 meters) tall and 2 feet (60 centimeters) wide, made of concrete-and-sawdust slabs. Plastic netting on the ceiling provided roosting surface for bats. Our primary design criteria were that the roosts had to be cheap, maintenance-free, easy to build, and able to withstand the tropical climate and termites for years.
We deployed the roosts in an agricultural pasture/forest mosaic landscape and, for comparison, in a protected primary forest, eventually installing 70 artificial roosts. We were astonished at how quickly bats colonized the artificial roosts. The first bats usually moved in within a few weeks – sometimes a few days – of installation and the colonization was mostly permanent, both in the forest and in deforested areas.
To estimate the bats’ impact on seed dispersal we used seed traps, simple wooden frames covered with fine nylon mesh, set out at night in a grid around roosts and at control sites away from roosts. Significantly more seeds were dispersed around artificial bat roosts than at control sites. The bats dispersed seeds of over 60 different plant species, and their preferred food items were fruits of pioneer plants that grow rapidly in open areas and are important vital for natural reforestation.
Kelm and his colleagues have demonstrated that artificial bat roosts can attract fruit-feeding bat species into deforested areas and significantly increase seed inputs around roosts. They plan now to produce a manual so others will be able to successfully build and install the roosts to spur natural reforestation elsewhere.
BCI members can read the whole story of artificial roosts and reforestation in the Summer issue of BATS magazine. To support BCI scholarships that fund this kind of invaluable research around world, please contact firstname.lastname@example.org.