Upstream, the river glides past, a liquid mirror reflecting the overhanging alders. Here, tumbling over rocky ledges, swirling around boulders, it fizzes with bubbles. There must be a dozen wriggling riverfly nymphs attached to the underside of the first rock that I lift from the water. When these stone-clingers are washed into the collecting tray, they squirm with convulsive energy, then settle: a broad head, a yellow, flattened body, legs with brown zigzag tiger stripes, a trident of tail filaments, abdominal gills beating furiously, extracting oxygen from the water. They are yellow May duns, common mayflies in this stretch of river and, along with stonefly nymphs, are here because the water is clean and well oxygenated. And dippers are here because they are here.
I watched a pair courting on this spot in early February. First the female arrived, fanning her tail, fluttering her wings. Then the cock bird, an operatic tenor in immaculate evening dress: black plumage, spotless white bib, chestnut cummerbund around his portly midriff. Drawing himself up to his full stature, stretching his neck skywards, he delivered an avian aria that I could hear above the tumult of the river. Sometimes, his startling white eyelids closed. Blinking, cleansing the eye surface? Or winking, sending a signal?
The late James Alder, a Northumbrian naturalist and artist, spent a lifetime watching dippers and, while ringing them, devised an ingenious technique for studying the mechanics of their blinking behaviour. He discovered that he could “hypnotise” them by stroking their heads, until the drowsy bird’s white-feathered upper eyelid winking movement was slow enough to photograph. Then, by blowing softly into the eye, he could record the rapid sideways sweep of the nictitating membrane – a sort of third translucent eyelid – that cleaned its surface.
Dippers have been building a nest nearby, under the riverbank, for a while now. One bird is back at these rapids this morning. He or she (their plumage is identical) lands on a rock, performs its territorial bobbing routine, then walks into the current and disappears underwater. It will be flipping stones, catching yellow May duns probably. When it bobs up again, swimming like a duck, effervescent silver water droplets rolling off its back, it has a beakful.
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