Birds Flap Their Wings?

How is it possible that birds can fly together effortlessly? How can they stay in sync, in perfect formation, and evenly spaced? How hard do they practice to get this good? Or do birds just fly? Is this what is meant by the effort of "no effort"?

Do we have to practice to move together effortlessly? Or is it the harder you practice the harder it becomes? What happens when you let go? Will it become softer? Does the chi keep us in sync?  Is this what is meant by the effort of "no effort"?