Geese honk while in flight to enable communication and encourage the flock to maintain a "V" formation. Goose teamwork is imperative in preserving the "V" formation, which is most aerodynamic for the flock.
Geese use honking as a form of communication within the flock for bonding, mating, displaying aggressive behavior and maintaining flight patterns. Geese honk from behind to encourage those in the front of the "V" formation to sustain speed.
Geese continually honk in flight in order to keep up communication with the flock, encouraging stray birds to maintain correct speed and distance to preserve a "V" formation, enabling the geese to conserve energy and fly for longer distances due to a drafting effect.