Dippers

A January walk through Strid Wood found a pair of dippers in one of their usual spots near the Cavendish Pavilion, prime dipper habitat of fast shallow water that provides an abundance of invertebrate prey on the river bed, lots of convenient rocks as mid-stream perches and nest sites hidden in the bank among the roots of riverside trees.

Further upstream, at the other end of the woods, a second pair was in residence on the rocks below the turreted aqueduct that provides their best nesting site along that stretch of river with the nest placed deep in a clump of grass on a ledge half way up one of the pillars, well above the highest flood level and safe from terrestrial predators.

Bridges provide popular nest sites and thirty years ago I found my first dipper’s nest jutting from the stonework above a ledge on the small bridge over Dicken Dike, just before it joins the Wharfe after flowing down from the Valley of Desolation. It was dark green, made of moss, domed with an entrance underneath from which dangled a few strands of grass from the lining, the structure vibrating as the parents, still bringing in moss and grass, worked inside it.

That nest was also well above any potential high water mark but that was not the case with a more recent one placed at the foot of a pillar of the bridge at Barden which, perhaps the work of a less experienced, younger pair, did not survive a rise in water level.

Dippers are essentially birds of fast hill streams and in Wharfedale their strongholds are in the north with few records downstream of where the Washburn joins the Wharfe to the east of Otley. After 15 years of bird surveys on the Wharfe below Harewood I have yet to see one there despite some stretches appearing shallow enough.

Millions of years have transformed these rotund perching birds, with their buoyancy reduced by solid bones, blood with a higher concentration of red blood cells to carry extra oxygen enabling them to stay submerged for half a minute, eyes with an extra protective eyelid and lenses that change curvature to focus underwater.

At times they explore the river edges, at others they dive and fly underwater using their wings like penguins, then walk on the bottom by grasping stones while turning over others to disturb small invertebrates. Even their shape helps for, by walking against the current with head downwards, the water flowing over their bowed back presses it to the river bed.

They are true miracles of evolution, birds capable of competing with fish for underwater prey, perfectly adapted to their watery niche.

Denis O’Connor