Tiny microplanes with unique "morphing" wings have been developed by engineering students in the Netherlands - based on studying the flight of swifts.
Their bird-based design makes them much more agile than standard aircraft.
The RoboSwifts, which have a wingspan of 5cm (2in) and weigh just 80g (3oz), mimic the swifts' abilities to change the shape of their wings in flight - potentially allowing them to be highly manoeuvrable at both very high and very low speeds.
The team of students from the Department of Aeronautical Engineering at the University of Delft based their work on the findings of tutor David Lentink, who has made detailed studies of swifts' flight.
He told BBC World Service's Digital Planet programme that, by changing the wing shape from fully extended to fully swept back, the swifts are able to improve their glide performance.
"We were wondering if we could apply this to improve small microplanes which are the same size as a swift," he said.
Dr Lentink's research found that during its life, a swift flies the equivalent of five times the distance to the moon and back.
To do this, the swift has to be highly efficient, and so has "morphing" wings which allow it to take advantage of prevailing flight conditions.
Similarly, the RoboSwift has feathers to shape-shift the wing, to reduce its area and to sweep the wing back.
This reduces air drag and makes the flight more efficient.
Dr Lentink said that trying to copy the swifts had presented a number of challenges, however.
"One of the big difficulties with simulating airflow at these speeds and these small sizes - birds are small and they fly quite slowly compared to airplanes - is that the physics involved is very different," he said.
"How can one capture this best? The software right now is not ready to handle this well, so what we did was combine experiments with numerical models."
The RoboSwift is controlled in flight by a user on the ground wearing a head unit that shows what the "eyes" of the plane - actually two wing-mounted cameras - can see.
The wings are then activated via remote control, which steers the craft by making small adjustments to the position of the wings.
RoboSwift team member Jan Wouter Kruyt said that at different flight conditions and different speeds the body of the bird can be adjusted putting it at an advantage over fixed-wing aircraft.
Aircraft did use flaps, which was an improvement, but morphing the whole wing "makes things much more efficient", he said.
'Swing wing' planes like the Tomcat are not as efficient as swifts
"The birds are really agile and they fly extremely fast and it will be pretty difficult for a pilot to steer the aircraft such that it can follow birds in real flight," he added.
"Perhaps human reaction speed will not suffice in controlling the aircraft."
Nevertheless, the team is hopeful that the lessons they learn can be applied to the design of future aircraft.
"There's a lot to be learnt from the birds - this is just the first step," said Mr Wouter Kruyt.
"We chose the nicest bird we could find - a real acrobat, a really efficient flyer - and there's a lot more to be learnt, perhaps also from different birds."