Bats and Sleep
Why do bats sleep upside down?
Bats hang upside down all the time except when they urinate and
defecate. To the question why they hang upside down?
An simple answer is that they have evolved in that way. Hanging upside
down is advantageous to them that why that behavior is retained in
the course of evolution. Then 'What are the advantages of haning
There are two main advantages.
1. Bats are nocturnal animals. They go in search of food during the
night time. Their night time activity protects them from many of the
day active predators. In the night, bats have to protect themselves
only from a limited number of night active predators (like cats,
snakes, owls, night jars etc). A simple and best way to stay in the
ceiling. The best way to stay in the ceiling is to cling on to the
roof of the ceilings. where bats can not be reached easily by their
2. The food resources for them are limited. From what ever little
food they get they have to efficiently budget their total energy for
maintaining their basal metabolism, flying, reprodution etc. Birds
being powerful fliers, have well developed chest and wing muscles and
spend more energy to take off from the ground - against the
Bats avoid spending most of their energy for the taking off by hanging
upside down in high raised ceilings. As they drop down from the
ceiling they start flying. This could be an "intelligent" adaptive
strategy to conserve energy. Instead of taking off from the ground
level (which needs lots of energy to lift the body against the
gravity) "evolution" has tried a different strategy in bats - to live
hanging upside down (to conserve energy)!
From a wildlife bioligist colleague:
"They need to drop into flight so this position sets them up for that.
Their feet are designed to grab and hold but their forelimbs are wings and
have very little holding capacity. The feet work so well at holding on that
a bat can die and will remain hanging by its feet.
...because the forelimbs are adapted for flight the back limbs have to carry
the load during rest. Gravity being the way it is, hanging by the feet is
the only option. Using the thumb claws they can climb effectively and
maneuver while not flying but the thumbs can't hold the full body weight for
any length of time without the feet helping."
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Update: June 2012