The linear flight formations of migratory birds are called echelons. The V and the J structures are typical and are the most readily recognized flock echelons, but other variations also occur. Studies of several species have shown that a true V-shaped echelon is, in fact, less common than a J formation is.

Fluid dynamics and energy wave configuration calculations have been used to test predictions of where birds should position themselves in relation to others to conserve the most energy as they travel through the air. Analyses of flock formations using photography have measured bird positions and found them to almost always be located such that they gain some energetic advantage. The animals are not very often in the expected optimal location, however, indicating that other factors also influence position in the formation.

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.

Answer originally posted Feb. 23, 2004.