Electricity travels from a place of high voltage to low voltage, just like water travels naturally from high elevation to low elevation. If the bird sits on a wire and also touches the ground, a path is created that allows electricity to travel through the body and to the place with no voltage. When electricity travels through the body of the bird in this fashion, electrocution takes place, and the bird dies. However, if the bird touches a single wire it does not get a shock because electric current passes through the wire instead of the bird.
