A paper published online in the Journal of the Royal Society Interface “tested the hover performance of 26 hummingbird wings from 12 different species in a machine that measured the torque and lift the wings produced at various angles.”
Researchers at Stanford University and Wageningen University found out that the bird’s “efficiency comes from the ratio of the wing’s length to its width.”
The ScienceShot article reporting on the research goes on to say:
“The power needed to sustain a hummingbird midhover is highly dependent on the bird’s wing aspect ratio. During the down stroke, wings with a larger aspect ratio (3.5 to 4.0 for hummingbirds) use significantly less power than wings with smaller aspect ratios.”
The study also compared hummingbirds to tiny flying robots. The researchers “found that the aerodynamic performance of hummingbird wings is ‘remarkably similar’ to that of an advanced microhelicopter rotor. But the wings were up to 27% more efficient."