The importance of these swirling, vortices of air trailing off wingtips in a flock of birds is wonderfully revealed in Fred Bodsworth's book, "Last of the Curle

The importance of these swirling, vortices of air trailing off wingtips in a flock of birds is wonderfully revealed in Fred Bodsworth's book, "Last of the Curlews." After reading this book, you realize how physics and billions of years of evolution not only brings wings into the world, but also magnificence. "Occasionally one of the curlew's wings would bite into the harder, spiraling air of a vortex left by the the wingtips of a migrating shorebird ahead of him, for even the passage of another bird left a trail in the air that the curlew's delicately sensitized wings could detect. Usually this alteration in the air pattern was the curlew 's first warning that he was overtaking a flock of birds ahead. When he found one of these vortexes, the curlew took advantage of it and followed it with one wing riding the updraft edge of the horizontal column of spiraling air. In this way he found a degree of lift readymade for him and his own wings could work a little easier. But no other shorebird except the golden plover flew as fast as the curlew did, and each time he slowly overtook the bird producing the vortex ahead. First he would hear the faint twitter of a flock's flight notes, the vortex would grow stronger, then the birds would appear as blurred figures against the grey sky in front. The curlew would fly with them for a time, but his greater speed would gradually drive him ahead. Then once more he would be flying alone."