The V and J echelons are also useful for members of the flock to keep an eye on one another for safety and support. On trans-continental journeys, support from the flock is crucial. Birds will adopt this type of formation in a crosswind. The strength of the wind determines how wide the formation flies. In high wind, the long side will usually be longer and fly straighter behind the leader, while the short side will fly wider with fewer members, sometimes as little as 2 or 3 birds.
This is due to the pressure areas being affected by the strength and direction of the prevailing wind. The reason the long side is into the prevailing wind is due to the way wingtip vortices work. At the wingtip, the low and high-pressure areas, respectively above and below the wing, come together, creating a vortex. The direction that the vortex spirals is up, over the wingtip, and in towards the body. A crosswind coming from the right will keep the vortex from the right-wing in a tight spiral.
This helps to maintain the integrity of the vortex for longer, so more birds can use it. The vortex from the left-wing, however, is spiraling into the wind. As such, a short distance behind the leader, its rotation begins to slow down, undermining the integrity of the vortex, and with it, the added efficiency. Birds will seldom fly directly into the wind , but even more rarely, fly with a direct crosswind, depending on the wind direction and speed, and of course, their destination. Birds will usually find an angle that takes advantage of the lift generated by a slight headwind.
This angle can be adjusted to balance the benefit of an easy flight with the haste to reach the destination. Studies show that the benefit of the additional lift, generated by wingtip a vortex, increases for each bird in turn. This was proved using heart rate monitors and GPS trackers on a flock of Ibis. The GPS locators were able to keep track of the position of each bird in the flock and its location within the formation.
At the same time, the heart rate monitors were able to record which of the birds was expending the most or least amount of energy. This study also brought to light some other interesting facts about the way birds behave while flying in formation. The common misconception of the flock following along behind a set leader, like ducklings behind their mother, was proved false.
The data showed that birds change position as often as once a minute. This changing of position allows the flock to share the losses and gains from the more and less efficient locations to fly within the formation.
Unsurprisingly, the vertex of the formation was proved to be the most taxing position to fly, and those behind benefit from the leader breaking the air. Interestingly what came to light was that the birds bringing up the rear are having a significantly easier time than those towards the front.
This shows that the passing of each bird adds to the high-pressure area, and theoretically, birds could actively work to increase the pressure by flapping their wings in the right place.
Further leading to the assumption that the larger a flock is, the more efficiently they fly together. Upwash exploitation and downwash avoidance by flap phasing in ibis formation flight.
All rights reserved. Why do some birds fly in a V? Here is the standard explanation for the V-formation: As a bird flaps, a rotating vortex of air rolls off each of its wingtips.
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The leaders of formations change from time to time, but the causes, frequency and characteristics of these changes have not yet been determined. Sustained observation from the ground of flocks covering great distances in the air is very difficult.
There are plenty of intuitive predictions about leader choice that quickly come to mind relative to the age, experience, sex, condition and social status of the leaders, but researchers have not figured out how to overcome the prohibitive logistic issues to test them. Some scientists have trained birds to fly in formation with small aircraft; perhaps their experiences will yield opportunities to test these ideas.
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