Bird flocks are ruthlessly efficient convoys, though that is not always obvious from the ground. As thousands of birds fly overhead, it is not immediately apparent that they are maneuvering at remarkable speeds or turning on a dime. Enough of this amateur description, however. Let’s turn this thing over to the expert—in this case, Richard Wilbur: As if a cast of grain leapt back to the hand, A landscapeful of small black birds, intent On the far south, convene at some command At once in the middle of the air, at once are gone With headlong and unanimous consent From…