Until n Unless there is a potential difference, current doesn't flow. This is the reason. The birds standing on the electric line stay safe because they are on either of line. When they will touch the other line(wire)..definitely...The Final Destination..! This is just like a resistor kept hanging in the circuit without any termination.

The simple thing - there potential drop across the points at which the bird's feet are touching the wires is less than what it'd take for the current to overcome the resistance offered by the bird's body.

The potential drop between the two points is minimum ideally zero therefore birds dont feel any current passing through them. The current will pass through their body but nothing will happen to them.

There are two cases in which bird will get electrocuted
first if one leg of the bird is at one phase and other leg is at other phase

second if one leg of bird is at one phase and other leg is touching ground.


Its not only the case with birds we as humans tend to feel absolutely nothing if we sit on single - phase. strictly speaking i have seen this in my country where people tend to work on live wires and absolutely nothing happens to them .