@Joseph Dabby yes exactly. When the bird is standing on the cable. Just one phase. The electricity still runs through the bird. But since it isn't contacting something else, like a different phase or ground, the bird becomes in the same potential plane as the cable. This is called Equal Potential Plane. The "energy" comes from different potential. This is why if there is a downed elctical line you can be shocked or electrocuted by walking near the cable. This is called step potential. Because the potential energy between to places on the ground is different the energy moves through the person.