Bats Boom on Organic Farms, Study Says

John Pickrell in England
for National Geographic News
February 2, 2004

Organic produce, grown on farms that steer clear of typical pesticides and chemical fertilizers, is becoming increasingly popular. Now, new studies of British bat and insect numbers bolster claims that organic farms are popular with wildlife too.

Bat activity may be up to 60 percent greater on organic farms than conventional farms in the United Kingdom, according to a new report. The study also revealed that one endangered European bat was completely absent on non-organic farms tested. A second study, to be published later this year in the science journal Conservation Biology, reveals that insect families which are key to British bat's diets are significantly more abundant and diverse on organic farms.

"Theoretical links between bat declines and the intensification of agriculture have been suggested, but until now there has been little solid data to back up those claims," said Liat Wickramasinghe, a zoologist at the Mammal Research Unit of Bristol University, England, and lead scientist behind the studies.

Though the findings are specific to the U.K., they have implications for insect-eating bats in any intensively farmed part of the world, she said.

Evidence of Declines

Bats' small size and shy nocturnal habits make them a challenge to monitor. But growing evidence suggests that European bats are declining. Six of the U.K.'s 16 species have special action plans in place for their conservation.

The greater horseshoe bat (Rhinolophus ferrumequinum), for example, has disappeared from much of its one-time range in England. Some experts believe its population has declined 90 percent during the 20th century, said Wickramasinghe.

Agricultural intensification has been suggested as a major cause of these declines—more than three-quarters of the U.K. is now farmland. This increased agricultural output has gone hand in hand with the increased use of insecticides and chemical fertilizers, but at the expense of biodiversity.

One report argued that out of 28 farmland birds studied, such as the grey partridge (Perdix perdix), 24 have shown range contractions linked to agricultural intensification since 1970. Insect declines have also been evident, said Wickramasinghe, a particular concern as Britain's bats are insectivorous.

In contrast to conventional farming techniques, organic farms in the U.K. limit the use of chemicals, and are controlled by strict certifying bodies. This makes them an ideal comparison for testing the impact of agricultural intensification.

Acoustic Sampling

As they report in the December Journal of Applied Ecology, doctoral student Wickramasinghe and biologist colleagues at Bristol University measured farmland bat abundance on summer nights in 2000 and 2002. The team used novel computer methods for recording the echolocation calls of bats and identifying them to species on 24 pairs of organic and conventional farms in England and Wales. "Being tiny, fast-flying, nocturnal creatures, it is impossible to get accurate abundance measures of bats directly," said Wickramasinghe.

Continued on Next Page >>


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