Hummingbirds, tiny but powerful, are truly enchanting to watch. They elegantly and swiftly dance between flowers, teasing our eyes with flashes of emerald green, ruby red and midnight blue before hovering to a stop as they slurp up nectar with their narrow beaks. You can even hear the drone of their wings beating an astonishing 70 times per second, on average.
But what’s the secret to their aerobatic abilities? Nobody has been able to figure this out before, so scientists from the University of North Carolina at Chapel Hill and Vanderbilt University put their heads together and endeavored to find out. After running detailed 3D simulations of hummingbird flight, they soon found out that there’s much more to it than just speedy wings. According to the study, which has been published in the Journal of the Royal Society Interface, these masters of flight actually move much more like insects than other birds.
To reach this conclusion, the scientists closely scrutinized the wing movements of a female ruby-throated hummingbird by placing spots of non-toxic paint on her wings. They then stalked the bird as she floated around an artificial flower using four high-speed video cameras that ran at 1,000 frames per second. After extracting data on the position of the dots in 3D and reconstructing her wings, the team used super-computers to create a fluid-dynamic model that simulated the thousands of invisible vortices in the air that were created as the wings flapped. Not only is the result truly captivating to watch, but it also revealed how these remarkable aerobats keep themselves in the air.
You might think that their trick is just to beat as hard and fast as they can; after all, some hummingbirds can flap their wings 200 times per second. But the simulation shows it’s much more complicated than that. To generate the lift necessary to hover and dart from flower to flower, the birds use small instabilities in airflow that are created as their wings flap.
During the downstroke, tiny vortices of air are formed around the wings that then combine into one, larger vortex, creating an area of low pressure underneath the wing. Air then floods in to equalize the pressure, generating the lift needed to maintain a hover.
But the birds also have another trick up their sleeves; they can generate lift on the upstroke. Larger birds put most of their effort into the downstroke, using virtually no force when they lift their wings back up. Hummingbirds, however, put more effort into the upstroke than most birds. They do this by rotating their wings as the front of the wing moves backwards, essentially causing them to invert, or flip. This means that the leading edge can create a vortex as it moves backwards, once again generating the low pressure needed for lift. This is much more similar to what we observe in insects, such as dragonflies, than most birds.
Alongside quenching our thirst for knowledge, learning about these amazing fliers could one day help engineers play catch-up with nature and build more efficient flying machines.