Today I looked out my window just as some little brown bird landed on one of the lines strung between the telephone poles, and I thought, “How long passed between the time the first human strung a wire like this and the first bird landed on it? Hours? Minutes? Do birds even realize that those handy landing sites they find all over are anything other than just another part of the natural world?”
I too, wonder if their concept of a power line is any different than a tree branch. Is there enough of an electro-magnetic field in a power line to make that differentiation? Or is it simply that it provides them a field of view unobscured by leaves? Or is it just random and we just don’t notice all of the birds perched in trees?
In cold weather, the wires are slightly warm. Which might be a benefit, but wires are also fully exposed to rain & wind, while inside foliage provides some protection for those.
I suspect predator birds like to perch with an unobstructed view, but birds that are more prey prefer to hide in foliage. OTOH, AFAIK, most of the mature birds that get killed by another animal are killed by ground-based predators, not other birds. Not all, but most.
In all, I bet the answer is not long, and no, to the degree they think at all, they “think” of wires as just a different kind of tree, not something utterly different.
They probably also “think” there’s no category difference between a bluff or cliff vs. a tall building.