Birds shorten wing strokes to save energy in formation
A new model suggests that birds flying in a V-formation cut their energy use principally by reducing the depth of their wingbeats while exploiting the wake of the bird ahead.
Birds flying in formation may save energy primarily by shortening their wing strokes, rather than simply gaining extra lift from the bird ahead, new research suggests.
Scientists at Brown University developed an aerodynamic model to investigate how a following bird interacts with the swirling wake produced by a leader’s wingbeats. Applying it to Northern Bald Ibises, Geronticus eremita, they calculated that a well-positioned follower could reduce its total mechanical power requirement by around 11%.
The most significant change was in the follower’s wingbeat amplitude. The model predicted that it could reduce its tip-to-tip wing movement by 28% compared with the leading bird, effectively using shallower strokes while still producing enough lift and thrust to remain in level flight.
The follower also held its wings slightly less extended during the upstroke, but this adjustment was considerably smaller. The researchers concluded that reduced wingbeat amplitude was the principal way in which aerodynamic assistance from the leader was converted into lower energy expenditure.
Large birds flying in a V-formation position themselves behind and to one side of the bird ahead, where they can encounter rising air generated beyond the leader’s wingtip vortices. This upwash is known to reduce the cost of flight, although the precise way birds use it has remained uncertain.
The new model indicates that the benefit is not simply a matter of the wake supporting more of the follower’s weight. It also reduces the thrust the bird must generate and the work involved in moving its wings through the air.
In the Northern Bald Ibis simulation, the follower generated 96% of the lift but only 83% of the thrust required by the leader. The power associated with producing lift fell by 9%, while that associated with wing movement and aerodynamic resistance fell by 18%.
Position and timing were also important. The most efficient follower flew approximately 0.88 m to the side of the leader, closely matching measurements from live Northern Bald Ibises. It also flapped half a wingbeat out of phase with the bird ahead, helping its wingtips remain aligned with favourable structures in the leader’s wake.
This synchronisation, known as wingtip path coherence, allowed the follower to gain useful lift and forward force while avoiding parts of the wake that would increase drag.
The researchers also extended the model to a six-bird formation. Although the second bird gained the greatest advantage, substantial energy savings were predicted farther back as each follower adjusted its position, wingbeat timing and stroke amplitude to exploit the wake of the bird immediately ahead.
The model simplifies both the birds and their wakes and considers individuals holding fixed positions, unlike the continually changing formations seen in natural flocks. The predicted 11% power saving nevertheless falls within the 10–15% range estimated in previous studies of large birds flying in formation.
July 2026
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