How could a bird be helped by the bird in front of it?
Every flapping wing leaves moving air behind it. Each wingtip curls the air into a swirl, and just outside the wingtip that swirl pushes air upward. This rising air is called upwash. A bird that flies slightly behind and to the side of another bird can, in theory, ride on that rising air and get some lift for free. Directly behind the leader the air is pushed downward instead, which is a bad place to fly. [1]
A simple way to picture it is a surfer riding a wave. The picture is only a picture: air is invisible, and the flow around a flapping wing is much messier than a wave. For many years the idea was widely believed, but the team behind the 2014 ibis study wrote that it had not been backed by solid evidence from real flying birds. [1]
Did anyone first measure energy savings in a V?
In 2001, researchers studied great white pelicans (a large species) that were raised by people and trained to fly in a V. The scientists measured the birds' heart rates, which give a rough estimate of how much energy the body is using. The birds saved a significant amount of energy when flying in formation, and the authors suggested that this may be a main reason large migratory birds evolved to fly this way. [2]
A magazine summary of the study says the savings were up to about 11 percent, with the birds at the back showing lower heart rates than the leader. Since that figure comes from a second-hand summary, it is safest to think of it as "roughly a tenth". [3]
Do birds in a V position and time their wingbeats to catch rising air?
In 2014, a team studied northern bald ibises, a large migrating bird, that had been trained to follow a small aircraft piloted by a person. Each bird carried a recorder that logged its position and the path its wingtips traced. [1]
The birds in the V took up positions close to where theory says the most upwash would be. Their wingtips also moved in step with the bird ahead, which would let them stay in the rising air through the whole flap. The bird flying directly behind another flapped out of step, which may help it avoid the downward air. [1]
The authors concluded that the birds must somehow sense, or predict, the swirls made by their neighbors. That is a careful way of saying what the data suggest. It does not prove that a bird "calculates" anything. [1]
If the leader gets no help, who has to lead?
A 2015 team followed young northern bald ibises on a migration in which people guided the birds. They found that the longer a bird spent in the lead, the longer it also spent flying in the moving air behind another bird (its wake). The birds appear to have swapped the lead position frequently, and the authors suggested this is a case of direct reciprocity, which means taking turns so that things even out. [4]
The word "cooperation" here is the authors' interpretation of the pattern. The study does not show that a bird plans to repay a favor. What it does show is a pattern: the lead seems to be shared among the birds rather than held by one bird all the time. [4]
How much energy does a bird really save in a V?
In 2024, a team fitted migrating ibises with precise GPS loggers and, on some birds, heart-rate loggers. The study followed 29 juvenile birds in a migration in which people guided the birds, with flights at an average of about 44 km/h (about 27 mph). When a bird flew in another bird's wake, its movement-based energy estimate and its effective wingbeat rate went down, the wingbeat rate by about 3%. In two of the five heart-rate recordings the researchers saw a drop, and the largest was 4.2%. [5]
Look at the title of the paper: "Small energy benefits of in-wake flying in long-duration migratory flights." The saving is real but small, and 4.2% was the biggest drop, not an average. Pelicans and ibises are different birds flown under different conditions, so the numbers should not be lined up as if one were right and one wrong. Over a migration that lasts many days, a small saving might still add up, though the study did not measure the total saved over a whole migration. [5]
Does every bird gain from flying close to others?
No. A 2011 study put GPS and motion sensors on pigeons flying in tight, shapeless flocks, not in a V. Pigeons flapped faster when they flew near other birds, especially directly behind them. Unlike the pelicans, they showed no sign of an aerodynamic bonus, and flying in a crowd may even cost them extra effort. [6]
So the V may work best for big birds flying steadily, not for everyone. One scientist quoted in a magazine suggested that in smaller formations of smaller birds, the swirl left by a bird ahead might fade away quickly. That is one researcher's view, not a settled conclusion. [3]
How could you watch a flock and test the idea yourself?
If you spot a V or a slanted line of large birds, watch from a safe spot such as a garden or yard, a park, or a pavement or sidewalk away from traffic. Does the lead bird change? Does the shape of the line shift? These studies were done on big birds like pelicans and ibises, so a flock near your home may do something different. Seeing nothing is also a result. Never look straight at the sun, and do not step into a road to follow birds.
If you want to read further, the abstract of the 2014 Nature paper [1] and the 2015 PNAS paper [4] are good places to begin.