Britain's busiest refuelling stations

Every autumn, hundreds of thousands of waders and waterfowl pour out of the Arctic and down the western edge of Europe. For many of them, the journey is not a single heroic flight but a series of hops between favoured estuaries, each one offering food, shelter and a chance to rebuild fat reserves. Our indented coastline, with its wide mudflats, sandbanks and sheltered creeks, sits squarely on the East Atlantic Flyway — the aerial motorway linking breeding grounds in Greenland, Iceland, Svalbard and Arctic Russia with wintering coasts in Britain, Ireland, Iberia and West Africa.

An estuary is a strange place to make a living. Twice a day the tide empties it, then twice a day it drowns it again. That rhythm, repeated over millennia, has created one of the most productive habitats on the planet — and a bird travelling two or three thousand miles has evolved to exploit it with astonishing precision.

The larder beneath the mud

At low tide, an estuary is a vast open-air pantry. Silt and clay particles lock in organic matter, and that matter feeds staggering numbers of invertebrates: lugworm and ragworm, Baltic tellin and cockle, mussels, mud snails and the shrimp-like crustaceans that waders find so irresistible. A single square metre of mud can hold thousands of tiny animals, and a feeding knot or dunlin may probe the surface 20 or 30 times a minute to find them.

Different bills mean different menus, which is why estuaries support so many species at once:

• Curlew and bar-tailed godwit use long, curved or slightly upturned bills to reach deep-burrowing worms.
• Knot and dunlin work the surface layers in dense, shifting flocks, often closer to the water's edge.
• Oystercatcher hammer or prise open mussels and cockles with a chisel-shaped bill.
• Redshank and grey plover pick at small prey in the wetter, softer mud, plovers watching rather than probing.
• Shelduck, wigeon and brent geese graze eelgrass, algae and saltmarsh plants where the mud gives way to green.

For a bird that may have lost a third of its body weight crossing an ocean or a ice cap, that abundance is the difference between reaching Africa and never leaving Britain.

Reading the tide like a local

If you take one thing from this article, take this: on an estuary, the tide is the whole show. Birds do not simply sit still and wait — they follow the water's edge as it retreats and advances, feeding on freshly exposed mud, then retreating to a roost as the flats flood.

The practical consequence is that a rising tide usually brings birds towards you. Aim to be in position around two hours before high water and stay for an hour after, when waders and wildfowl pack tightly into saltmarsh, shingle banks and the upper shore, often in plain view. Spring tides push them closest and produce the most dramatic concentrations; neap tides leave birds scattered and distant across the flats. Cold snaps and hard frosts also drive birds off inland fields and onto the estuary, so a sharp January morning can transform a quiet scene into a spectacle.

What you might see, and when

Estuaries reward repeat visits far more than one-off trips. The cast changes week by week, but a loose seasonal rhythm holds true:

• July to October: the great wader return. Adult knot, dunlin, black-tailed godwit and greenshank arrive first, followed by juveniles into autumn. This is when a good estuary feels genuinely alive.
• September to December: wildfowl move in — wigeon, teal, pintail, shelduck, and brent geese fresh from the Arctic tundra. Pink-footed geese flight out to roost in noisy skeins at dusk.
• December to February: peak numbers. Estuaries such as the Wash, Morecambe Bay, the Dee, the Humber and the Severn hold internationally important counts, and anyone can contribute to the national monthly wetland counts that track them.
• March to May: birds moult into breeding plumage, gathering in tight, noisy flocks before heading north. Black-tailed godwits turn brick-orange; dunlins acquire black bellies.

Practical fieldcraft for a better visit

You need less kit than you think, but the right kit. A pair of 8x42 binoculars handles most situations; a telescope is a genuine advantage on wide estuaries where roosts sit 300 metres away. Wear wellingtons, take a tide table, and never turn your back on a flooding channel — estuary mud and fast water are far more dangerous than they look.

Then there is behaviour. Waders operate on tight energy budgets, and every unnecessary flush costs them calories they cannot spare. So:

• Use hides and sea walls, and keep to the upper shore rather than walking out onto the flats.
• Give roosts a wide berth, especially on high spring tides when birds are already stressed and crowded.
• Keep dogs on a lead near the tideline, and move away quietly if a flock takes flight.
• Pick up litter, particularly fishing line and plastic, which tangles in mud and in birds.

Do that, and you will be welcomed back by the same curlews next winter — which is, in the end, the whole point of looking after these places. An estuary that still fills with birds each autumn is a working landscape, and one of the finest free wildlife spectacles in Britain.