Question

Why does birds sitting on high tension coir does not get a shock

Answer 1

There are two parallel transmission lines on high tension coils the potential difference between these two lines is about 240V throughout their lengths. If you connect any conducting device across these two wires it causes current to flow between the wires. When the bird atnds on high tension coils there is no potential difference between the legs of the bird because it stands on a single wire. So no current passes through the bird. Hence it doesn't feel any electric shock