Given the task definition and input, reply with output. In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

How many birds migrate in flocks?, 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.
most