Can high voltage power lines EM provide power for drones?
This is definitely a fun one, because the closer you get to the power lines the more power you can extract. It's not dangerous to touch the lines at one point while away from the ground, so the best solution may be to have a quadcopter-like craft with a clamp-on current transformer "claw" extending from it. The current generated could be considerable. Random example transformer. That one generates a current that's about 1% of that in the primary - but in this case the primary could be >1000A! Easily enough to fast-charge a small or medium sized drone.

Fly for a bit, then cling to the wire like a bird to recharge.