There are two reasons: 1. The wire is insulated (like the cord that goes to a table lamp), so the bird never touches the part with the electricity. 2. Electricity goes from one place to another, like from the pointy end of a AA battery to the flat end. The bird on the wire is only touching one part of the electrical circuit, like only touching the flat end of the battery. There is no where for the electricity to flow, so the bird is not hurt.