Wet weather puts bats off flying as they don’t like getting wet, according to the findings of a study published in the scientific journal Biology Letters.
A wet bat needs more energy to fly because damp fur provides less protection than when dry. Wet fur also affects the bat’s aerodynamics, which in turn also costs energy. Until now scientists thought bats avoided rain because there was less prey to catch and because raindrops affected the bat’s echo-finding capability.
The study observed 10 Sowell’s short tailed fruit bats (Carollia sowelli) in Costa Rica. The bats weigh just 18 grams, live from eating fruit rather than hunting insects and frequently encounter rainfall in their natural environment.
The researchers exposed the bats to three treatments in outdoor enclosures including dry conditions, moist fur without rain and moist fur with rain. Energy usage was calculated by measuring the content of the non-radioactive isotope C13 in the air exhaled by the bats.
The findings indicate that rain as such does not force the bats to use extra energy. However, wet fur led to the bats using twice as much energy compared to dry conditions. The researchers conclude the reason is probably because wet fur provides less protection from cooling.
“Bats with moist fur lose so much heat that they need to burn more energy to maintain a steady body temperature,” says Christian Voigt, one of the study’s authors.
Wet bats are also less aerodynamic and must use more energy to compensate. In dry conditions a bat’s smooth fur covers the animal, making it aerodynamically efficient. That changes when the fur becomes damp. Taking flight in the rain is only worthwhile for a bat when the energy it can ingest replaces that expended by flight.
