According to a miltary.com story DARPA's "Power Line Urban Sentry" (PLUS) program is developing small electric UAVs that rely on the public power grid for navigation and power. When their batteries run low, the UAVs land on high tension power lines and steal power to recharge themselves. During recharging, they morph into shapes that appear natural, such as pigeons or trash. Once regarged, they'll morph back into flying robots and take off. The robot also store maps of the power grid, allowing them to navigate visually should their GPS signal be lost or jammed. For details see the SITIS entry for the SBIR Energy Harvesting for Small Air Vehicles proposal or the DOD SBIR description.