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American Association for the Advancement of Science

Bats eat as many bugs as birds do

Little bats have big effects: Myotis elegans is one species of insectivorous bats who protect plants in Mexican coffee plantations from pests.

Insects are fast food for birds flying through tropical forests, which munch on them all day long. But things aren’t much safer for the bugs at night, two groups of scientists found out recently. It turns out that bats eat lots of insects when the sun goes down in the forests. In fact, they may eat as many insects as the birds do during the day.

How did the scientists figure this out? They used nets to cover up certain parts of the forest during the day and night. After that, they counted the number of bugs living under the nets during the day, protected from hungry birds. Then they counted the number of bugs living under the net at night, safe from snacking bats.

The studies showed that bats eat just as many insects as the birds do, and that both birds and bats play an important part in keeping the forests from being overrun by bugs. When the bats can’t reach the insects under the nets, the bugs have a huge feast of their own and eat up a lot more the forest’s leaves than they normally would, according to Margareta Kalka of the Smithsonian Tropical Research Institute and her fellow researchers.

Kimberly Williams-Guillén and other scientists from the University of Michigan, who looked at bats, birds and bugs on a coffee farm in Mexico, say bats are important for the crops that humans grow. Without enough bats around to eat insects, the insects might eat too many of the crops—like coffee bushes—that people plant for themselves.

The two bat studies appear in the 4 April 2008 issue of the journal Science.