For years it was thought that the main reason bats don't fly in the rain is because the mass of rain droplets are obstructing their flight. As part of a series of trials in Costa Rica, scientists studied Sowell's short-tailed fruit bats, which they exposed to rain like effects. They observed the rain itself though it's droplets mass didn't affect the bat's mechanical flying behavior whatsoever. What made it really hard for them, however, was the fact their fur and wings were wet, and like most mammals, bats have to keep themselves warm by patting harder, coupled with the fact that water is mussing their silky fur and dampening their wings, bedraggled bats might also be less aerodynamic.
Study source/Photo Source.
