The hovering hummingbird is halfway between insects and birds when it comes to flight, aerodynamic research published in Nature magazine reveals.
Hummingbirds are renowned for their flying skills
Many experts had argued that the bird flew just like a big insect, getting equal lift between down and up strokes.
But the new study shows the hummingbird cannot fly in quite the same way because its wings are less flexible.
In fact, the bird gains 75% of its lift from the wing's downstroke, with the other 25% provided by the upstroke.
This makes it different from other birds which rely solely on the downstroke to stay airborne.
Douglas Warrick, of Oregon State University in Corvallis, US, and colleagues trained rufous hummingbirds (Selasphorus rufus) to hover while feeding from a syringe filled with sugar solution.
They used a sheet of laser light to study the air currents generated by the birds' wings in a mist of microscopic oil droplets.
They found that hummingbirds have not been able to evolve the symmetrical hovering achieved by insects, because their wings, built from feather and bone, are less flexible.
But they are the undisputed exhibitionists of the bird world, being able to hover for sustained periods, with food, and fly backwards.
Interestingly, the flapping motions they make with their wings bear a striking resemblance to that of large insects such as hawkmoths which are of a similar size.
It illustrates how different animals have evolved similar design plans to cope with the rigours of flight.
"The basic physics of how you can hover at a flower apply to both," Dr Warrick told the BBC News website.
"Birds started off with bone and feathers - bird wings and bird muscles. As a result they haven't converged completely; they don't do it exactly the same as insects. In biology that's a major theme."
He said the hummingbird could serve as a useful model for engineers seeking to build small, flapping aeroplanes.
"You can probably learn something about building a machine from the way nature builds a machine," he said.
"The one big caveat is that an engineer can start from scratch - biological evolution doesn't ever start anew. It's encumbered with the trappings of one's ancestry."