Most birds that flit through dense, leafy forests have a strategy for maneuvering through tight windows in the vegetation — they bend their wings at the wrist or elbow and barrel through.
But hummingbirds can't bend their wing bones during flight, so how do they transit the gaps between leaves and tangled branches?
A study published today in the Journal of Experimental Biology shows that hummingbirds have evolved their own unique strategies — two of them, in fact. These strategies have not been reported before, likely because hummers maneuver too quickly for the human eye to see.
For slit-like gaps too narrow to accommodate their wingspan, they scooch sideways through the slit, flapping their wings continually so as not to lose height.
For smaller holes — or if the birds are already familiar with what awaits them on the other side — they tuck their wings and coast through, resuming flapping once clear.
"For us, going into the experiments, the tuck and glide would have been the default. How else could they get through?" said Robert Dudley, a professor of integrative biology at the University of California, Berkeley, and senior author of the paper. "This concept of sideways motion with a total mix-up of the wing kinematics is quite amazing — it's a novel and unexpected method of aperture transit. They're changing the amplitude of the wing beats so that they're not dropping vertically when they do the sideways scooch."
Using the slower sideways scooch technique may allow birds to better assess upcoming obstacles and voids, thereby reducing the likelihood of collisions.
"Learning more about how animals negotiate obstacles and other 'building-blocks' of the environment, such as wind gusts or turbulent regions, can improve our overall understanding of animal locomotion in complex environments," noted first author Marc Badger, who obtained his Ph.D from UC Berkeley in 2016. "We still don't know very much about how flight through clutter might be limited by geometric, aerodynamic, sensory, metabolic or structural processes. Even behavioral limitations could arise from longer-term effects, such as wear and tear on the body, as hinted at by the shift in aperture negotiation technique we observed in our study."