Highly agile airborne drones with flexible wings inspired by seagulls could be used for surveillance within the narrow confines of cities.

The US air force has long been interested in "morphing wing" aircraft that can change their shape in mid-flight to carry out different tasks, such as rapid dives or slow gliding for loitering over an area under observation.

Now researchers at the University of Florida in Gainesville, led by Rick Lind and funded by the USAF and NASA, have built a prototype remote-controlled drone with a seagull's ability to hover, dive and climb rapidly. To achieve this level of agility, seagulls flex their wings at both the shoulder and elbow joints.

The 24-inch prototype drone uses a small motor to control a series of metal rods that move the wings. One rod connects the fuselage to the mid-point of the wing, while another connects this rod to the wing's ...