Why do birds land on live wires and don't die?

In order to receive a shock you must touch one wire and the ground or one wire and the "ground" wire. Electricity flows in a loop between wires and you must contact two wires at the same time. When a large bird, like a pelican or something with a long wing span lands on the wires and accidently touch one of the other wires while they are standing on the other one they do get electrocuted and die. The wires are usually far enough apart so they can't touch two at the same time. If there is a wire that falls on the ground and someone on the ground touches the wire, then they can get electrocuted and die. You have to complete a circuit to get a shock.