Bats always sleep upside down hanging from a high and secluded spot. The biological characteristics of bats make it necessary for them to sleep in this fashion. Bats cannot launch themselves into flight from the ground, like birds do. This is because their wings are not as powerful as that of the birds and they cannot produce the necessary lift for starting a flight. The hind legs of bats are also not strong or developed making it possible for them to run and gain the momentum for flight.
Hanging upside down gives bats an ideal position to take off into a flight when necessary. They can just let go and on their fall through the air they will get the necessary momentum for taking off into flight.
Hanging upside down also hides the bats from predators. Besides, they don't have to exert any energy to hang upside down because of the unique way their talons are formed. It is just their weight on the talons that keep it closed around the surface where they are locked. As long as the bats are relaxing in this position, the talons cannot open and the bats will not fall off.
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.
Well, they do sleep like that but, when they are awake and upside down they are most likely getting ready to take off. They take off from a hanging position, drop down into flight.
