Why Do Bats Hang Upside Down?

A bat has the ability to go into a form of hibernation at will ... this
is called TORPOR. When cold weather reduces feeding opportunities, and
threatens physical harm, the bat can opt to "sleep" through the cold.
When the bat is in torpor, it must use as little energy as possible, to
maximize the use of its body fat for surviving through the cold period.
It can't waste energy using muscles in its extremities to hold onto a
perch!

Over time, the bat has developed a special kind of foot joint that lets
it lock its foot in a tightly clasped position, with the weight of the
body keeping the foot locked. By hanging from a safe and secure perch,
and locking this joint, the bat can drift off into a torpor without
worry of falling. Since it does not need to use any muscle to hold it's
grip the bat can "sleep" for as long as its body fats can sustain it.

So, all of these puzzle pieces can help to explain why bats hang upside
down. This upside-down, locked-in posture enables bats to huddle
together in safety, preserving body heat, avoiding predators, and
hibernating until more favorable conditions allow feeding to resume. At
the same time, the posture does allow for the bat to drop free of the
crowded mass of the roost, and unfold its large wings and glide into
flight.

Over many years, bat species have developed a way of life that includes
a hanging posture as one of many survival skills. They have also
developed other special skills, like the ability to find flying insects
in the dark with ultrasonic echoes, or rotate their heads 180 degrees so
they can see behind them while they hang in their roosts. Their bodies
have adapted to allow them to fill a niche they have made for themselves
in the natural world. It also provides another marvelous aspect of
Nature's variation for us to wonder at.

There are few animals that depend on flying for moving about as much as a bat does. While birds and insects fly, too, they can manage to walk about if they have to. But the limbs and feet of a bat are not suited to walking, which means they also cannot stand easily.

So when a bat is in its roost; the easiest thing for it to do is to hang on, head down!
The bat does a great many things that are quite remarkable. To begin with, the bat is a mammal the only mammal that can fly. The young are born alive and feed on milk from the mother. When the young are very small, the mother may carry them with her when she goes hunting!

Since they have to hunt for their food, you would imagine that bats would need exceptionally good eyesight. But actually, bats do not depend on their eyes for getting about. When bats fly, they utter a series of very high-pitched sounds. These sounds are too high to be heard by the human ear.

The echoes from these sounds are thrown back to the bat when it is in flight. The bat can tell whether the echo came from an obstacle near by or far away, and can change its course in flight in time to avoid hitting the obstacle!

Most people think all bats behave more or less the same way, but since there are more than 2,000 kinds of bats, you can see why this is not so. There are bats with a 15-centimeter wingspread and bats with a wingspread of nearly 2 meters.