Why don't birds fry on electric lines?

[MJDale]

After talking non-stop in the car today about electricity wires, my young son asked: Why is it that birds can sit on a wire without electrocuting themselves?

[Luma]

It's all a question of Potential Difference. If I were to stand on the ground (potential 0 volts) and then proceed to hold a live conductor (let's say, potential 230 volts), the potential difference would be 230 volts.
The bird on the overhead wire however is sitting on a conductor with a high potential (eg 11,000 volts) but because the bird isn't touching the ground or anything else for that matter, there won't be any potential difference. So the bird can sit there happily all day without getting itself plated.

[Bahbill]

As already stated, without a potential difference there cannot be a current flow, and it is current flowing through the body (heart) that electrocutes.
When you are in an aeroplane you can be at several thousand volts when airborne but as everything around you is at the same potential, so you do not feel any difference.

[Sensei]

Without babbling about technical stuff, which I would guess your young son wouldn't care about....to have electricity flow, you need a place for it to come from and a place for it to go. To accomplish this, the two points need to be connected in some way. A bird sitting on ONE wire is not connecting the two points, so no roasted foul. Similar to screwing a light bulb in partially, no current will flow until you screw it in far enough for both points touch the bulb. The bird would need to touch two wires to get electrocuted.