Birds on a wire don’t get an electric shock. Let’s see why.
Birds can sit on power lines without getting electrocuted, even though the wires are not insulated. For a current to flow through a bird on a wire, there would have to be a potential difference between its two feet. The wire might be at a very high potential [voltage]. But, as the bird has both its feet touching the same wire, so there is no potential difference between the bird’s feet.
If the bird could stand on the wire and touch any other object such as the ground or another wire then there would be a potential difference between the wire and the other object. As a result, the current would flow through the bird’s body and the bird would get a big electric shock.