What’s the News: Bats have to use twice as much energy to fly when they’re wet as when they’re dry, a new study in Biology Letters found, which may help explain why many bats refrain from flying in heavy rain.

How the Heck:

The researchers captured ten Sowell’s short-tailed bats in Costa Rica.
Each of the bats flew around a large outdoor cage in three different circumstances: dry, wet (the researchers dampened their fur and wings with tap water) on an otherwise dry day, and wet on a fairly rainy day.
By measuring the bat’s metabolism, the researchers found that wet bats expended twice as much energy during a short flight as dry bats did (twenty and ten times their resting rate, respectively).
The wet bats didn’t weigh more than the dry ones, ruling out the idea that the damp bats simply had to work harder to carry extra water weight. Nor did already wet bats burn more energy flying on a rainy day than a dry one, meaning the problem isn’t that raindrops mess with the bats’ flight mechanics.
The researchers suggest two other explanations: Being wet might cool the ...