The passage is structured like which of the following?
PASSAGE – I
The passage below is followed by a question based on its content. Answer the question on the basis of what is stated or implied in the passage.
Migratory birds often move in linear flight formations called echelons. Typically, we find V and J-type structures, which are the most readily recognized flock echelons, nevertheless other variations to these major patterns can also be found. A true V-shaped echelon is, in reality, less common than a J formation, studies conducted on several species reveal.
Why do the birds fly in formations? Two well-corroborated and complementary explanations are available right now. A major idea is to save energy by capitalizing on the upwash vortex fields generated by the bird wings in the front. The second - to facilitate the job of orientation and communication among the flying birds. These two explanations are not necessarily mutually exclusive, and in fact, both are supported by many studies. The relative importance of each of them, no doubt, changes as various factors, like the season of the year or the reason behind individual flights, change. During local feeding flights meant to locate food, for instance, careful orientation and collision avoidance are probably much more important than the conservation of energy. However, during long-distance migration, though orientation and communication remain important, but the case for conservation of energy by optimization of its position holds greater importance for each bird in the flock.
Where should the birds position themselves in relation to others to conserve the most energy as they fly in the air? Fluid dynamics and energy wave configuration calculations supply the answer. Analysts, using photography, have determined bird positions and found them to almost always be located to enable the bird to earn some energetic advantage. However, the birds are not always at the expected optimal location, indicating that other factors also come into play.
Researchers have used the knowledge of birds, visual axes, "blind spots" and visual fields to pinpoint the best locations for a bird in a flock to maintain optimal visual positioning. The actual positions are usually having a positive correlation with these predictions but are, again, not always perfect. The positions of birds have been classified and it has been found that some individuals occupy positions to satisfy the energy conservation principle; others enjoy better visual contact placement, while the rest do not apparently respond to either benefit or are in a position so as to gain some advantage from both the benefits available.