Birds get the credit, but bats eat more bugs

Maggie Fox, Yahoo News 3 Apr 08;

Bats play a bigger role than birds do in controlling tropical insects, and the loss of bats might mean that morning cup of coffee gets more expensive, researchers said on Thursday.

Two separate studies show bats eat far more insects than birds do, protecting plants of the rain forest and, in one of the studies, coffee plantations.

The studies, published in the journal Science, suggest that the loss of bat populations worldwide might affect agriculture -- not to mention make warm evenings outside more uncomfortable, the researchers said.

"Bats are impacting ecological systems in all kinds of ways, and I just want them to get the credit they deserve," said Kimberly Williams-Guillen, a tropical ecologist at the University of Michigan who led one of the studies.

Williams-Guillen and colleagues studied bats at Finca Irlanda, a 740-acre (300-hectare) organic coffee plantation in Chiapas, Mexico.

In previous studies of insect damage, scientists have simply covered plants to keep off birds and then counted the bugs and measured what they ate. They forgot to account for what the bats did at night.

Williams-Guillen and her colleagues set up three types of enclosures -- one that only excluded birds, one that only excluded bats at night, and nets that kept out birds and bats day and night.

During the summer wet season, the coffee trees under the nets that kept the bats out had 84 percent more insects, spiders and other bugs than unprotected plants, they reported.

Birds had far less of an effect, they said.

HANGING OUT ON PLANTS

Margareta Kalka of the Smithsonian Institution in Balboa, Panama, and her team did a similar experiment in what she described as pristine rain forest.

"Insects could freely pass through the nets to eat the plants, hang out on the plants," Kalka said in a telephone interview.

"Both bats and birds had a significant effect on plants. And in our particular study ... we found a bigger impact of bats than from birds," Kalka added.

Plants shielded only from birds during the day had double the insect damage of plants that were uncovered, Kalka said. But plants netted at night to keep bats out had three times the usual insect damage.

The findings have important implications for conservation, Kalka said.

"Bats worldwide are suffering," she said in a telephone interview. "People still don't understand what are the threats to bats. Climate change may be a threat to bats."

Williams-Guillen's team agreed.

"Bat populations are declining worldwide, but monitoring programs and conservation plans for bats lag far behind those for birds," they wrote.

Williams-Guillen also noticed that bats do not only catch insects on the fly -- a technique that helps them eat half their body weight in a single night.

Many also perched upside-down from branches, swooping onto nonflying insects and other pests as they munched on leaves.

Kalka said it is clear why people credit birds with protecting crops.

"People like birds better and they are more obvious -- they are colorful, they are singing," she said.

"People love them -- they see them eating bugs off leaves. It seemed more obvious that birds have a role in pest control. Bats hunt in the dark so it is really hard to study them. They are completely overlooked."

(Editing by Will Dunham and Xavier Briand)