Hovering only a splash above the bottom of the weir, a jiggling ball of flies catches the eye of a bird on a stick. It dashes across. One false flap might cast it down to drown into the churn, but there is really no need for my heart in my mouth.
How is supreme agility possible in a creature encumbered with an appendage of feathers as long as its body? The grey wagtail shows the exceptional manoeuvrability of any flycatching bird, its tail transformed into a pliable rudder. In one action it drops, dips, flips, jinks and flits, giving shrill peeps as it shoots full-beaked through the willows in an undulating flight of apparent exuberance.
Among the UK’s three species of wagtail, the grey lives up and down to its name more than the others. Neither the migrant yellow nor the resident pied wagtail exhibits quite such an exaggerated bob. The regular tail-dipping of their waterside cousin is as inevitable as breathing.
Below the railings on the next bridge is a scatter of banded demoiselle wings – compelling evidence that a second pair of breeding wagtails here are stripping off the inedible parts of damselflies before feeding them to their young in a crevice nest nearby. Sure enough, one of the pair appears, alighting on a raft of waterweed in the middle of the river. The moment it comes to rest, it sets off in motion. Up flips its tail, as high as its head, maybe higher. Down, up, down, keeping a rhythm with its rear. All the while the head stays steady, beak leading the hunt.
After a few seconds of stillness, the bird’s beating tail starts to lose momentum, until it is reduced to a quiver. That slowing seems to be the cue to go, for the wagtail suddenly springs and makes for the opposite bank; the same rolling flight of peaks and troughs. It lands on a precipitous riverside ledge, where a steadying pause might be in order. But no, off goes the tail again, conducting its own beat. Not drowning but waving.
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