Many bats spend their resting hours hanging upside down.
The position looks exhausting to us.
For a bat, it can be remarkably efficient.
Bat feet can lock onto a perch
When a bat lands and lets its body weight pull downward, specialized tendons in the feet help the toes tighten around the perch.
The grip can remain secure with very little muscular effort.
That is why a sleeping bat does not need to consciously squeeze the branch all night.
Hanging gives them an easy launch
Many bats are not built to take off from flat ground as easily as birds.
Their wings are excellent for flight, but their hind limbs are relatively small.
Hanging high gives them a solution.
Let go.
Drop.
Open the wings.
Start flying.
Why roost high up?
High roosts also provide some protection from predators.
Caves, trees, bridges, and buildings can offer dark secure places where large numbers of bats gather.
Do all bats hang upside down?
Most familiar roosting bats do, but bat species vary enormously.
Not every species uses identical roosting behavior.
Does blood rush to their heads?
Bats are small enough and have cardiovascular adaptations that make the upside-down posture manageable.
What would feel terrible to a human is normal bat anatomy.
Is this like horses sleeping standing up?
Both are examples of animals resting in positions that seem uncomfortable to us because their bodies are built differently.
Horses can sleep standing with help from a specialized support system in the legs.
Bats use a locking grip and gravity.
For many bats, upside down is less a weird sleeping position than a very convenient parking system.
And that’s the short explanation.
Related explanations: Why do horses sleep standing up?, Why do owls turn their heads so far?, and Why do birds fly in a V formation?