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How do bats hang upside for so long without any adverse effects, such as poor blood circulation? The Chameleon

Bats spend the daylight hours hanging upside down in a secluded spot, such as the roof of a cave or the inside of a hollow tree, safely hidden away from predators and inclement weather. Hanging up high has another advantage: bats can’t run and launch into flight like birds can; instead they drop into the air straight into flight.

Their bodies have a number of adaptations to deal with this topsy-turvy lifestyle. For example, they have specially adapted feet for hanging upside down. If we want to grip onto something with our hands we use our muscles to close our fingers around it, but the tendons in bats’ feet and legs work the opposite way round. Bats have to flex muscles to open their grip, and the talons shut when they relax. The weight of the bat locks the foot into a tight but effortless clasp. This means bats don’t use any energy when they hang upside down and their grip remains constant, even after death.

In most mammals, the knees bend forwards. This would be awkward for bats hanging against a surface, and their knees bend the other way. Many bats have a flap of skin between the legs which they use to catch bugs, and their backward-bending knees form a basket to hold their prey. Bats’ respiratory and cardiovascular systems are also adapted for the high energetic demands of flight. The heart is up to three times as large as that of a non-flying mammal of a similar size and they can increase their heart rate up to 1,000 beats per minute when flying.

Bats are also much smaller and lighter than us so they don’t experience the blood rush to the head that we would when hanging upside down. We have evolved to live upright and our circulation system reflects that. Our circulation system has one-way valves that prevent blood pooling in our feet and legs. Conversely, a bat’s large, powerful heart and specialised valves in its blood vessels prevent any blood pooling in its head. Evidently, bats have overcome any downsides to gravity as they can remain hanging upside down for weeks during hibernation with no adverse effects.