Scientists claim to have solved the mystery of birds’ seemingly effortless in-flight turns and the softness of their landing.

It is thanks to a small group of feathers called – alula – which helps form a small vortex of air at the tip, the scientists said.

Alula is a thumb-like structure at the bend of the wing, and birds use it in slow and steep flight such as landing.

The researchers observed the flight of magpies when the birds moulted the alula feathers.

"It’s not that they cannot fly without the alula. But with the alula they seem to turn more easily," said first author Sang-im Lee from Seoul National University.

Then the researchers moved on to the wind tunnel experiments where they visualised the movement of tiny particles around magpie wings.

Here they observed that a tiny vortex from the alula tip presses the air flow over the wing and makes the air flow better attached to the wing surface.

"For the wing to fly better, the air has to move closer to the wing. Although the alula is small, it creates enough vortex to prevent the air flow from being detached from the wing," Lee explained.

Measurements of the forces acting on wings in the wind tunnel proved that indeed the presence of the vortex from the alula helps the birds in flight.

The researchers aim to apply the way that the alula works in designing a device that enables the air vehicles to turn better and more efficiently.

The study was published in the journal Scientific Reports.