Antennalope are a stunning example of cross-species symbiosis. These North-American antelopes have evolved to have metal antennas on top of their heads, instead of the traditional antlers. They roam throughout the American plains, constantly on the move, migrating to where radio signals are weakest. Because their antennas relay radio signals, engineers have been able to use this natural resource to create transcontinental radio networks. The antennalope were featured in a 2003 ad campaign for Nextel long-range walkie-talkies.