Ever wondered why hummingbirds hum? Here's why

It is no secret that hummingbirds hum, but the phenomenon has baffled many. Do hummingbirds have vocal cords? How do they hum?

Scientists have now discovered the cause of the phenomenon.

In a study published in the journal eLife, scientists said that they knew that the sound from the birds was linked to the movement of the wings, based on "their understanding of aircraft wings and rotor aeroacoustics." But the primary differences are that the latter would not change shape or flap and also operate at much higher speeds. However, rotating around a centre pivot is what they have in common. They discovered that the aerodynamic forces and subsequent pressure changes produced as the wings move were the reasons behind the sounds.

This conclusion was arrived upon after carrying out experiments with a species known as Anna’s hummingbird.

The scientists set up two experiments to see how this happens. In the first setup, they put up 2,000 microphones and high-speed cameras in a cage with six hummingbirds and gave them an artificial flower to feed on one at a time. This helped them with developing a 3-D acoustic map that not only had the sound of the birds but also visuals of the movement of the wings.

In another setup, to figure the reason behind the sound, it was important to study the lift and drag of the wings. So the birds were surrounded with pressure plates and high-speed cameras. This helped them figure out the pressure forces and how they changed.

In the end, the results of these two experiments were combined. The results revealed that the speed and direction of the wings and the aerodynamic forces with the movement of the wings largely explained the hummingbirds’ hum.

Scientists also discovered that hummingbirds' wing movements are unique and while for most birds' sound is produced only in downward strokes, in a hummingbird it is for both upward and downward strokes. The wing movement of the hummingbird, which is also significantly faster, is unique because it follows a U-shaped smile.

The team applied a simplified version of their theory to data for flying creatures from mosquitoes to birds like pigeons to reveal why their motion produces different sounds.