they are indeed made of copper
Particularly the ones overhead railway lines.
There was an entertaining article on the beeb about a year ago about Cape Town's exports to China. 1. Fruit. 2. Copper. Hang on a minute. We've got no copper deposits here, no plants to get ore into metal....oh yeah, it's all stolen (aka 'recycled'). They now have a task team (called the 'Copperheads') who run around investigating cable theft particularly and have a pretty awesome success rate for SA investigations. Further proof that the theory of specialisation is a good one.
Around that time of the beeb's article, I had all the copper plumbing at the back of my house stolen, the garden tap from the front nicked and wandered out one afternoon to find a couple of little bastards in the process of stealing my water meter. Interestingly, since the copper price has deflated, my local scrapyard really isn't doing the business it once was. It's mighty quiet down there most days. And I replaced the plumbing with the non-copper variety so we're all happy except the thieving guys, who have now resorted to nicking the contents of people's cars, including their CDs, CD players and speakers. So I don't have sound in the jalopy any more now.