Bird on a wire?

Question

why is it that birds do not get electricuted while on power lines?

Answer 1

They will, if they complete the circuit. Martin has given a very good answer, so I will not add more.

Answer 2

because they are not grounded!!!

Answer 3

The bird does not complete the circuit.  If there is no loop there is no path for current to flow and electrocute the bird.  If the bird touched two wires, it would be in big trouble.

There are linesmen that work on the high power lines while they are still live.  A lot of the time it would be too expensive to shut off the power, so they actually fly to the lines on a helicopter, like a bird they don't complete the circuit.  One danger they do have to look out for is a potential difference between the helicopter and the line.  They will negate this by using a metal rod (holding by an insulated part) to reach out and touch the energized line, equalizing their potential.

I don't think I'd want to do that job!

Answer 4

For the same reason that a lamp doesn't light up if you connect only one side a supply to it.  For anything interesting to happen the other side of the supply must also be connected to the (other side of) the lamp.

The cable upon which a bird sits is just one side of a supply.