Why bats generally get electrocuted on transmission wires?

All of us might have noticed that the bats (flying fox) will be hanging upside down and mostly get electrocuted. Why bats generally get electrocuted on transmission wire? But if we see the other birds, they will not die by electrocution while sitting on transmission wires. To understand this fact we have to observe two reasons –

First how the morphology of bats is different from other birds
How does electrocution happen

How morphology of bats are different from that of birds

First of all, it is to be understood that the bat doesn’t come under bird species. Bats are actually mammals, which like any other mammal give birth to offspring instead of egg-like birds. They are flying mammals like Flying Squirrel, Colugo, or Gliding Possum. But the major difference of bats from any other flying mammals is that bats can have “Sustained Flight” whereas others can have short time flight.

Now during flying they resembles the birds however, the way they fly is very different from the birds. Unlike birds, bats do not flap their entire forelimbs. Instead bats flap their digits which are long and covered by a thin and delicate membrane or patagium to fly.

Another difference of bats as compared to birds is that since their hind legs are underdeveloped, unlike birds. They cannot run in an upright position to launch a flight and also their wings are not strong enough to generate a sufficient lift.

Due to these reasons, bats will hang upside down and instead of running to get into the flight, they fall into flight. Before falling to flight they have to extend their patagium or wings enough to produce a drag like a parachute.

How does electrocution happen

When the bats are hanging from the transmission wire, they accidentally touch the two wires of transmission cables due to their way of flight.

If we observe the transmission wires, there will be 3 wires. All these 3 wires carry voltage/current which are in different phases. That is, all the 3 wires are at different voltages. When a bird sits on a wire, the legs of the bird are at the same voltage level. Hence, in absence of any voltage difference, there is no current flowing through the body of the bird. Because for current to travel, there should be a potential difference between two connected points.

But in the case of bats, their patagium will touch the two nearest wires which are at two different potentials. That is the two connected points (i.e patagium) are at different voltage levels, causing the current to flow.

If any living being will be touching two different potentials, i.e two wires at different voltages or a live wire and earth, then the current will try to flow through the body and that living being will be electrocuted.