Taking a walk around the neighborhood, I was treated to one of the great sounds of late fall, the honking of Canada Geese in flight. Looking up, I saw a small V of geese heading south. Have you ever wondered why these geese fly in V-shaped flocks? Such flight formations yield a significant savings of energy.
As a bird flies, eddies of air swirl off the tips of the wings. Some ornithologists began to wonder if trailing birds could take advantage of these upward eddies to gain lift. Using a computer model developed by aviation engineers, these ornithologists found that birds flying in V’s could realize an energy savings of 71%, compared to birds flying alone. The model showed that greatest benefit would result when a trailing bird has a wing overlap of about 5 inches with the next bird ahead. In other words, if a bird moved abreast to the next bird ahead of it, the wing of the trailing bird would overlap by five inches with the wing of the bird next in line. The model also showed that each bird except the leader should be between one and three yards behind the bird in front for greatest energy savings. Finally, the model shows that the birds in the flock should beat their wings in perfect synchrony.
Films of migrating Canada Geese were used see how well the positions of the geese agreed with the computer model. In many cases, the wing overlap was right around five inches, the most desirable position. Distance to the next bird and synchrony of flight were not always as predicted, probably because of turbulence in the air . Nevertheless, the performance of the geese suggested that an energy savings of 36% resulted from flying in V’s.
In a V of geese, the leader receives no benefit of the flight formation. Geese do switch positions so take turns as leader. The social status of the leader(s) has not been studied.
Canada Geese are not the only birds that fly in V-formations. Most geese species, including Snow Geese, fly in V’s. I’ve also seen Tundra Swans, White Pelicans, and Double-crested Cormorants flying in such formations.
Some ornithologists have begun to use microtechnology to better understand the behavior of birds flying in V’s. Henri Weimerkirsch fitted migrating pelicans with heart rate monitors. He found that pelicans toward the back of flight formations had lower heart rates, demonstrating the advantage of mooching lift off of birds flying ahead of you.
Stephen Portugal provides even more remarkable data. He fitted endangered Northern Bald Ibises with small data loggers that recorded the position of birds and their flapping rate several times a second. The data loggers have to be recovered to collect the data. The Northern Bald Ibises were the perfect species to overcome this challenge.
Portugal and others were trying to reintroduce this species into central Europe where they had been extirpated. Portugal’s team raised young birds and taught them the old migration route by leading them in a microlight airplane. At the end of each day’s migratory leg, the ibises were captured and their data loggers were read.
The data showed that the birds are bang on with theoretical predictions: the birds beat in synchrony and the distance behind and to the left or right of the next bird in the V conform to the predictions.
Some ibises prefer to be on the left side of the flock and others on the right. They do switch positions frequently and take turns being the leader.
When the migration was first begun, the ibises did not fly in a regular formation. No adults were present to teach them how to fly in a V. Nevertheless, they quickly discovered on their own the advantages of flying in a V.
[Originally published on November 11, 2015]