  V-shaped and echelon formations help migratory birds to consume less energy
for migration. As the case study, the formation flight of the Northern Bald
Ibises is considered to investigate different effects on their flight
efficiency. The effects of the wingtip spacing and wingspan are examined on the
individual drag of each Ibis in the flock. Two scenarios are considered in this
study, (1) increasing and (2) decreasing wingspans toward the tail. An
algorithm is applied for replacement mechanism and load balancing of the Ibises
during their flight. In this replacing mechanism, the Ibises with the highest
value of remained energy are replaced with the Ibises with the lowest energy,
iteratively. The results indicate that depending on the positions of the birds
with various sizes in the flock, they consume a different level of energy.
Moreover, it is found that also small birds have the chance to take the lead
during the flock.
