HE other day, I had what I’m tempted to call a commonplace encounter with common swifts. In truth, most people attached to the most aerial of our summer migrants know that there is seldom anything ordinary about such an extraordinary creature. Five birds, possibly parents with chicks to feed, were assaulting the insects wafting up from a Derbyshire hillside of tall grasses and flowers. They scythed down over the slopes, the blade-like wings held dead level, as they exploited both the effects of gravity and the fresh breeze to spire and jink after unseen prey. Occasionally, one made a flight-line that cut slantwise across the current, so I could hear aing noise from the flight feathers, like the sound of air on an arrow fletch. For a split second, another let the wind take it sideways, as if it were momentarily losing control, the wings paddling hard, until finally
