Recycled boxes help bats to survive during heat-waves and increase rice productivity

 Adrià López-Baucells examining a bat

Adrià López-Baucells examining a bat

The Ebro Delta is a region known for its huge rice production. To protect the rice, farmers use bats since 1997 that would eat the pest insect species (chilo supressalis) which are known to strongly damage their fields. But the life of bats has become difficult since heat waves overrun bats in their sleeping-boxes. Biodiversity-researchers at the “Natural Sciences Museum of Granollers” in Barcelona examined thermic responses during over-heating events and tested a “cooling system” for the helpful animals. My Climate Service spoke to Adrià López-Baucells, one of the PhD students working on “Bat Ecology and Conservation“.

Since 1992, the Ebro Delta is one of three Spanish regions that has a “Protected Designation of Origin” for intensive agricultural rice production. The delta region of the Ebro River is situated in the Province of Tarragona, Catalonia, in northeastern Spain, on the Mediterranean Sea, close to the border of France. The “Cooperative of the Ebro Delta” produces 90,000 tons of rice annually, from 14 varietals, cultivated on 22,000 hectars. Andalusia and Extremadura are the major rice-producing regions, but the Ebro Delta has the advantage of stable water supply since it is a wetland region. Global demands are rising, but the threats are expanding as well: from the changing climate to pest infestations. To protect the rice by not using pesticides, bats are a natural preventer. It has been estimated that only one only bat can eat up to 1,000 moths and mosquitos per night. Nevertheless, wetlands lack natural roosting sites imperiling bat conservation and minimizing their potential ecosystems services. Therefore, farmers decided to put bat boxes on the fields. This cycle works very well - as long as the bat boxes would fulfill cooling measures for the bats during climate change scenarios.

The researches of the “Natural Science Museum of Granollers” are part of a “bat conservation-network” which is collaborating successfully with teams in Portugal, UK, Finland, in the Amazon, in Madagascar, Kenya and other countries. This study was financed and supported by the Government of Catalunya, a network of National Parks and different Spanish wine companies, among others.

Since climate change is noticeable it is necessary to rethink wildlife conservation actions to make them efficient and appropriate in the new context.

“The Ebro Delta has a great potential to carry out this experimental bat box study, as it is a huge wetland with plenty of and insects, including pest species in an area that is still assessable to do a research. Bats find great living-conditions here”, explains Adrià López-Baucells. They are not the first biologist-group: Bat boxes were installed in the fields several years ago (1997) by an external team. Unfortunately, they were never properly monitored, until farmers recognized that the bat boxes became full and that the surrounding rice area didn’t have the pest anymore. “We got notified, and then we started investigating about the role of bats as pest controllers. Therefore, Xavier Porres, a collaborator of the Museum designed a new recycled bat box, especially thought to fulfil the needs of the Ebro’s Delta farmers. He was using the chaff of the rice and vegetal fiber to create new bat boxes that would resist heat-waves and - it worked out.

 Bats sleeping in a bat box during midday (c) Oriol Massana & Adrià López-Baucells

Bats sleeping in a bat box during midday (c) Oriol Massana & Adrià López-Baucells

“You must adapt your techniques to the place and their people”

Adrià López-Baucells says: “For us, that was a great learning. We saw how the waste became useful again - and even helps local bats to find new roost sites. You always have to adapt the techniques you already know to the place and their people that you find. The new boxes were accepted by the bats immediately.”

But then, an unexpected heat wave in Northern Spain in August that lasted more than two weeks on a row made bat’s life unbearable. It is assumed that an overheating event might occur in bat boxes above 40 degrees. For bats, their response toward heat waves are quite unknown, but several cases of mortality events have been reported during the last years. “Night-active bats leaving the boxes in the middle of the day, probably because they couldn’t stand the high temperatures of over 50 degrees in their bat boxes. Some tried to find other boxes, but when it was not possible, they lay down and died”, Adrià López-Baucells says. In this study, about 15 different models of bat boxes were tested. In Europe bat boxes are usually black, out of heavy material, especially in colder Northern countries. “We saw that in warmer countries, the temperatures became much higher in the other models than in the box made from rice chaff.”

Bats became a symbol in the Ebro Delta

Taking into consideration the orientation, material and position of the bat boxes are key elements to avoid detrimental effects upon bat colonies. The lack of guidelines might be imperiling bat conservation, especially in warm countries where less work has been done. Placing a bat box in the wrong place might create an ecological trap to the animals due to the extreme temperatures.

Now, with all this knowledge and experience, the research-group is currently working to improve the new boxes and help bat populations in summer months. Meanwhile, the natural cycle is closed: the farmers help bats by providing recycled artificial roosts, and bats increase rice-productivity by controlling rice pests. Upcoming projects include preventing pests in wine-yards, pines and olive trees due to rising temperatures. “This project was well received and has a great potential worldwide”, Adrià López-Baucells resumes. “Farmers clearly see the value of the animals, they are proud of bats.” The demand of these bat boxes still increases, but it is always necessary to keep an eye of the changing conditions in all fields because one single adaption measure is never enough for the long-term conservation. “My message to others is: We need to improve natural habitats protection and those areas harboring natural roosts as well as promoting sustainable use of the landscape.”