The plowing and planting are done and the red tractor is moving across the field in midafternoon. The field is golden, and the sky is blue, over a vast expanse. Soon will come the harvesters- the giant green machines. Directly close behind are flocks of white feathered birds, yellow-eyed, determined, and closely-packed.  Their bodies move in waves a foot above the ground. The racing birds will stay a precise distance behind the machines as if stopped by an invisible wall from moving closer. With fixed determination in their bright yellow eyes, a geometric precision sustains the distances of the birds in flight- their distance from the ground, their uniform speed, and formation behind.