A few years from now, bird-watchers may be in for a double take: that flapping creature in the distance? Nope, not a bird. Mutant dragon fly? Nope--it's Darpa's latest unmanned aerial robo-sentinel, inspired by the flight mechanics of birds. The tech company Aerovironment recently won a $2.1 million contract to further their work on the Nano Air Vehicle (NAV). One of many progressive projects from Darpa (the Pentagon's advanced-research unit), the NAV is the first-ever "controlled hovering flight of an air vehicle system with two flapping wings that carries its own energy source and uses only the flapping wings for...