Scientists have finally discovered why birds fly in a V-formation
Scientists have long known why geese, ibises and many other birds fly in a V-formation during long-distance migrations: this formation helps them conserve energy. However, exactly how this effect comes about has remained a mystery until now.
Researchers at Brown University have put forward the most detailed explanation to date. It turns out that birds flying behind and slightly to the side of the leader can significantly reduce the amplitude of their wing beats thanks to the airflow created by the bird flying ahead.
Details
The study focuses on northern bald ibises (Geronticus eremita), which, like many other large birds, form a characteristic V-shaped formation during migration.
To understand why this formation is so efficient, the researchers created an aerodynamic model that simulates the interaction between two birds. It took into account not only the birds’ positions relative to one another, but also how the airflow changes after each wingbeat.
During flight, the tips of the wings create rotating air vortices. If the following bird positions itself correctly, slightly behind and to the side, it enters an updraft that helps it move forward.
Until now, researchers have debated whether this current provides additional lift or reduces air resistance. The new study shows that the main effect is a reduction in the need to generate its own thrust.
This is precisely why a bird can flap its wings much less vigorously. According to the model, the amplitude of the wing beats is reduced to approximately 70 per cent compared with solo flight.
As a result, the mechanical power required to maintain flight is reduced by approximately 11 per cent.
The authors note, however, that previous wind tunnel experiments had shown total energy savings of up to 25 per cent. The new model does not contradict these findings, but explains the physical mechanism underlying this effect.
To carry out their calculations, the researchers literally broke the flight down into a sequence of individual time steps. At each step, they determined the position of the vortices, the wings of both birds and the aerodynamic forces acting on them, before combining the results into a single picture.
The resulting model corresponded well with the results of previous experiments and, for the first time, provided a detailed explanation of how the leader’s wake makes flight easier for the bird following behind.
Why this is important
This work helps to better understand not only the behaviour of birds, but also the laws of aerodynamics.
The authors believe that the findings could be useful in developing control algorithms for groups of drones. If drones can utilise each other’s air currents as effectively as birds do, this will increase their flight range and reduce energy consumption whilst carrying out tasks, such as monitoring agricultural land or fighting forest fires.
Source
The study was published in the journal *Proceedings of the National Academy of Sciences* (PNAS).
Title: A minimal wake–vortex model explains formation flight of flapping birds.