Published online 29 April 2008 | Nature | doi:10.1038/news.2008.782


Artificial bat roosts could re-seed the tropics

Luring bats to new homes in deforested areas could help regeneration.

Bats help to disperse seeds in some tropical forests.Detlev Kelm

Conservationists are learning to harness a new weapon in the fight against deforestation: bats.

Bats have a crucial role in dispersing seeds from local plants in the neotropics — an ecological zone that includes South and Central America. Now, researchers have found that they can attract bats to deforested areas using artificial bat roosts, where the bats set up home and defecate the seeds of recently eaten fruit in their new neighbourhood.

Deforested areas of the neotropics are notoriously difficult to regenerate. After trees are chopped down so land can be used for plantations and cattle pastures, the resulting nutrient-poor soil is often unable to produce plants of any significant value, and so the land is abandoned. With no overhead cover and few food sources, abandoned plantations and pastures offer fruit-eating animals such as bats little reason to leave the safety of their forest home and defecate the seeds where they are needed most. This has led to extensive research into how seed distributors can be lured into open areas.

Past studies have tried planting islands of trees in open areas for animals to visit, and have even used fake fruits loaded with tasty juice to draw hungry bats in for a visit (see Fake fruits could help restore rainforest). Now, Detlev Kelm and colleagues at the University of Erlangen-Nuremberg in Germany have investigated the effect of artificial roosts.

Home away from home

Bats aren't deterred by the concrete look and feel of artificial roosts.Detlev Kelm

Kelm and his colleagues installed 45 bat roosts in the heavily fragmented forest–pasture mosaic lands of northeastern Costa Rica. They regularly inspected the roosts during the day, when bats sleep, to see how many had decided to move in. Bat numbers in the roosts varied from a single individual to about 100. “Counting sleeping bats is usually really easy, but as some roosts became particularly popular we had to start estimating,” says Kelm. “Animals like bats had no reason to visit abandoned lands, but with the right roosts we can clearly change this,” Kelm says.

Free-standing roosts made of sawdust concrete and standing 1.6 to 2 metres high, were most effective at attracting bats and lasted the longest, the researchers report.

Up to 100 bats can crowd into a roost.Detlev Kelm

The team found that ten different bat species used the roosts, but not all were fruit eaters. There were some nectar-feeding species, a few vampire bats and even a frog-eating species.

The number of vampire bats, viewed by locals as disease-transmitting pests, was fortunately very low and was restricted to the largest roosts in forest habitats. Roosts that were near agricultural land and smaller in size did not attract these pests. The nectar-feeding bats, by contrast, were a welcome find. As fruit-eaters and pollinators, they are doubly valuable for spreading seeds and pollinating plant species separated by fragmented habitats.

Spreading their seeds

When the team investigated the seeds defecated on the ground overnight, they found a huge improvement around the artificial roosts: 2.2 seeds per square metre per night, including 69 different seed types, compared with 0.4 seeds per square metre per night at deforested sites without artificial roosts. The results are reported in Conservation Biology1.

“This study not only shows how valuable bat ecosystem services are, but also how effectively these services can be manipulated to help in reforestation,” says bat ecologist Brock Fenton from the University of Western Ontario, Canada.


Fenton notes that the bats in this study were only relocated tens of metres from their usual habitat, but he wonders if they could be driven further into empty areas. “If we could ultimately manipulate bats into travelling [for] kilometres that could prove very useful,” he says. “I’m really curious as to how far we can ultimately get bats to go.”

There are, however, further hurdles in the way of forest regeneration, such as making sure that seedlings germinate and survive. “Fortunately, bats tend to eat the fruits of pioneer plant species that are quite good at growing in open environments,” says Kelm. “It is a taste that could ultimately serve the forest very well.” 

  • References

    1. Kelm, D. et al. Conserv. Biol. doi:10.1111/j.1523-1739.2008.00925.x (2008).
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