[ad_1]
Hummingbirds can be instantly recognizable by their namesake sound, but the cause of the feature has long been a mystery.
Now the researchers say they’ve solved the riddle, finally taking the “hmm?” out of hummingbirds.
David Lentink, assistant professor of mechanical engineering at Stanford University and co-author of the research, says that while buzzing was known to be related to wing movement, it was previously unclear what exactly was behind it. the sound. Pressure changes generated by the flapping, vortices in the airflow, and the hissing of the feathers themselves were just some of the possibilities.
Now, it seems that the answer lies mainly in the aerodynamic forces, and therefore the pressure changes, produced as the wings move.
“This is enough to really understand what the main source of the buzz is,” Lentink said.
In the journal elife, scientists from Eindhoven University of Technology, Sorama spin-off company and Stanford University report how they came to the conclusion after conducting experiments with a species known as Anna’s hummingbird.
In one setup, the team arranged more than 2,000 microphones, along with high-speed cameras, around a cage in which six hummingbirds fed on an artificial flower, one at a time. This allowed them to capture the sounds produced by the birds to create a 3D acoustic map visually linked to the movement of the wings.
To explore what caused the sounds, the team sought to measure the lift and drag forces produced by the flapping of the wings. To do this, they created another experiment in which the birds were surrounded by pressure plates, along with high-speed cameras, and watched as they soared. It took the size of the squeezing forces produced and how they changed over time.
When the researchers gathered the information about the forces and movement of the birds’ wings, they were able to predict the sounds that would be created from these factors alone. They then compared them to the 3D acoustic map produced from the microphone setup.
The results reveal that the aerodynamic forces produced when the wings move, as well as the speed and direction of wing movement, are more than enough to explain hummingbirds buzzing.
The team notes that a crucial factor is the movement of a hummingbird’s wings. While most birds only create lift on the downstroke – which the team considers the primary source of noise – hummingbirds do so downhill and uphill due to their unusual wing movement, which follows a path similar to a U-shaped smile. Plus, these hits happen much faster for hummingbirds – around 40 times per second. As a result, according to the team, the movement of the hummingbird’s wings generates sounds at both 40Hz and 80Hz – sounds that are well within our hearing range and have proven to be the dominant components of the humming noise. birds.
But the variations in the forces in the hits, as well as the additional influence of the movement of the U-shaped wing, generate higher frequency harmonics of these sounds.
“The beautiful thing about the intricate hummingbird wing stroke is that these two primary impulses also cause even higher harmonics,” Lentink said, adding that these tones added to the timbre of the overall sound.
“It’s really the specific way in which forces fluctuate that creates the sound we hear,” he said.
The team applied a simplified version of their theory to data on flying creatures, from mosquitoes to birds like pigeons, to reveal why their movement makes different sounds.
“It’s the way they generate forces that is different,” Lentink said. “And that explains why they scream against buzz, against buzz, against whine.”
[ad_2]
Source link