The study showed that during courtship flights, male hummingbirds sustain accelerations that would cause a fighter jet pilot to pass out.
Chris Clark, a biologist at the University of California at Berkeley, reckons that the pressures of courtship push males to the limit of what is physically possible.
Using high-speed video footage to study their flight, he has shown that, relative to their body size, male hummingbirds are the fastest moving vertebrates.
For the study, Clark tricked a number of males into performing their acrobatic courtship displays by placing decoy females close to their perches. To impress females, the males drop out of the sky in U-shaped flights.
Clark found that as they speed towards the ground, they travel nearly 400 times their body length each second. This is nearly twice the maximum speed reported for diving peregrine falcons and slightly faster than diving swallows.
As they approach the ground, the hummingbirds spread their wings and tail, letting them pull them up into a skywards glide.
At this stage, Clark calculated that their bodies undergo centripetal accelerations reaching 10 g -- a force equivalent to 10 times the gravitational pull of the earth.
At accelerations above 7 g, fighter jet pilots can pass out or temporarily lose their sight because their blood becomes unevenly distributed in their circulatory system.
"I think their small size makes hummingbirds relatively immune to passing out under high g," New Scientist quoted Clark as saying.
Their diminutive dimensions means blood pressure varies less from one end of their circulatory system to the other and is less affected by rapid acceleration. The hummingbirds also spend about one third of a second under high g; humans pass out after just a second under the same amount of force.
Photograph: Mike Blake/Reuters