In this paper,the flocking flight of Northern Bald Ibises(Geronticus eremita)and their induced drag during the flock are investigated.Northern Bald Ibises are long-range migratory birds.These birds fly in an echelon and Ⅴ-shaped formation,possibly to reduce their drag;therefore,as a result,they may save energy to fly farther.The aerodynamic drag forces of each individual bird and the flock are modeled theoretically.Extensive analysis shows how,during flocking flight,the drag force reduces as the size of the flock increases.Additionally,wingtip spacing effects on the total drag of the flock are investigated.The fraction of drag reduction of individual ibises is also analyzed.Four initial arrangement scenarios are considered for flocks of ibises of different sizes in this study.Two shuffling algorithms are applied for position switching and energy balanc-ing of the ibises during their flight.It is suggested that ibises can save energy by means of different arrangements of flock members during long flights.The results indicate that how different sizes of the birds can manipulate their positions to fly further and save energy during migration.