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

Key words: Drag, Echelon, Energy, Flock, Ibises, Wingtips spacing