Electricity naturally flows from places with a stronger electric force to places with a weaker electric force. But with a single power line, the electric force is nearly the same at all places along the line. This is why electricity doesn’t flow through the birds’ bodies.

Now imagine what would happen if a bird sat across two power lines with different electric forces. The shock from the powerful electricity passing through its body would kill the bird. When electricity passes through a body, we call it an electric shock. In the same way, if you were flying a kite and it hit a power line, electricity would flow from the high-voltage power line to the low-voltage ground and give you a serious electric shock. This is why you should never fly a kite near power lines.