Context: Many, if not most, birds migrate in flocks. For larger birds, flying in flocks reduces the energy cost. Geese in a V-formation may conserve 12–20% of the energy they would need to fly alone. Red knots Calidris canutus and dunlins Calidris alpina were found in radar studies to fly 5 km/h (3.1 mph) faster in flocks than when they were flying alone.

Question: How do most birds migrate?
Answer: in flocks

Question: How much energy do geese conserve flying in a flock?
Answer: 12–20%

Question: How much faster do Red knots and dunlins fly in a flock?
Answer: 3.1 mph

Question: How do birds conserve energy?
Answer: a V-formation

Question: What does flying in flocks reduce?
Answer: energy cost