V-formation Saves Energy

wide photograph of birds flying against a blue sky

Biological Strategy

Great white pelican

AskNature Team

Image: Nadiia Oborska / Shutterstock / Some rights reserved

Modify Buoyancy

Buoyancy is an upward force exerted by air or liquid on a solid object that works against the object’s weight. A hawk glides through air and a duck floats on water due to buoyancy. Some living systems (such as fish eggs) can remain sedentary and therefore maintain the same buoyancy at all times. But most must adjust their buoyancy because they can’t survive long unless they change position. These living systems require strategies to not only be buoyant, but also adjust buoyancy level. They often modify buoyancy by adding or decreasing lift, or by changing their weight. For example, birds like condors that soar for a long time shift the directional orientation of their wingtip feathers to manage buoyancy. Fish alter the amount of air in their swim bladders to increase or decrease their weight, thus altering their buoyancy.

Search this Function

Move in/Through Gases

Living systems must move through gases (which are less dense than liquids and solids) such as those in the earth’s atmosphere. The greatest challenge of moving in gases is that because the living system is heavier than the gas, it must overcome the force of gravity. Moving efficiently in this light medium presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag and increase lift so that they can stay aloft and take advantage of variable currents. Additionally, they must overcome gravity when moving from a liquid or solid into the air. The fairyfly, the smallest known insect, is a tiny wasp that must move through the air. To the wasp, air feels like a heavy liquid and to move through it, it uses special feathery oars rather than wings.

Search this Function

Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

Search this Living System

V-formation flight of great white pelicans conserves energy by each bird taking advantage of the upwake field made by the wings of the bird in front of them.

“Our results provide empirical evidence that, compared with solo flight, formation flight confers a significant aerodynamic advantage which allows birds [great white pelicans, Pelecanus onocrotalus] to reduce their energy expenditure while flying at a similar speed. In birds flying in formation, each wing moves in an upwash field that is generated by the wings of the other birds in the formation. Modelling has shown that when birds are flying with optimal spacing, a maximal reduction in power can be achieved and total transport costs can be substantially reduced. However, field observations of V formations indicate that birds often shift from their optimal positioning, perhaps in an attempt to maximize the aerodynamic advantage of flight formation, thus reducing the energy saving— so geese, for example, may make an energy saving of only 2.4%.

“In our study, pelicans often had difficulty staying within the formation, particularly when flying at the rear. But even though these birds were regularly adjusting their position, they still achieved a significant energy saving. This saving may be only partly due to effects of the wakes of other birds on the power input that results from formation flight itself. When flying in formation, pelicans appear to beat their wings less frequently and to glide for longer periods. A rough calculation based on our estimates of the proportion of time spent flapping and gliding in formation, and assuming that the overall costs of the glide–flap sequence is the sum of the gliding and flapping components, reveals an actual saving of 1.7–3.4% as a result of wake effects on power input — this value is comparable to that estimated for geese.

“The main benefit of flight formation, which until now has not been recognized, could be that by flying in a vortex wake, pelicans are able to glide for a greater proportion of their total flight time, with the total energy savings of 11.4–14.0% being achieved primarily through this strategy.” (Weimerskirch et al. 2001:697)