Bats are the only mammals that can fly, which makes them pretty cool. When they aren’t flying around, you will find many of them hanging upside down in structures such as caves. The floors of many caves are covered in ‘guano’ – accumulated bat excrement (poop and pee). But peeing when you are hanging upside down would be a messy business. If you have ever wondered how bats have a pee without getting it on their coat or in their eye, this YouTube clip is for you. Then, read on for a fuller explanation.
Hanging Upside Down

Like sloths, bats hang upside down to sleep.
©iStock.com/nymphoenix
Bats are not the only animals that hang upside down. You will also see sloths, parakeets, white-breasted nuthatches, chimpanzees, and many spiders doing it. However, bats are most famous for exhibiting this behavior. The question is, why do they do it?
The answer is connected to their ability to fly. Bats have very flexible wings that they can move in lots of different ways. Their bones are the same as the ones we have in our arms and hands. The most crucial part of their wings is the membrane between the sides of their body and their fifth finger. This provides both support and lift. However, it is not enough lift to get them off the ground.
When you see most birds take off, they use a run-up to get enough lift to get them airborne. Bats cannot stand on their hind legs, let alone run. Their leg bones have become very short and thin to save weight so that they can fly. The only other option is to take off from standing (like a hummingbird). Generally, bats rely on dropping from a height to become airborne.
Peeing on a Perch
Hanging upside down is all very well until you need a pee or poop. So, when the urge arises, the bat reaches up with its forelimbs to grasp whatever it is hanging from. For example, in an enclosure, this might be a rope. Then it can lower its rear end, urinate, and shake off to avoid any dribbles, which would be inconvenient. When finished, it lifts its legs back up to resume the hanging position. It defecates in the same way. Alternatively, bats also defecate and urinate while flying, which helps ensure they do not get waste on their coat.
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