Why the Estuary Demands a Different Eye

On an estuary, the usual rules of identification break down. Distances are deceptive, light is often flat and grey, and the birds themselves are the colour of the mud they feed on. A curlew at four hundred metres looks like a godwit; a godwit at six hundred metres looks like a small curlew. What separates them is the outline they throw against a pale sky or a sheet of water, and the call that carries across the tide. Learn a handful of silhouettes and four or five voices, and the whole estuary becomes readable.

Curlew and Whimbrel: The Long-Billed Pair

The curlew is our largest wader, and its shape is a study in curve: a long, evenly decurved bill, a hunched back, and long legs trailing well behind the tail in flight. Watch it fly and you will see slow, deliberate wingbeats on broad wings, often a loose line of birds rather than a tight flock, with white rump showing above the barred tail. Its voice is unmistakable — a rising cur followed by a falling lee, mournful and rounded. In spring, males add a long bubbling trill on the breeding grounds, a sound that lifts the heart.

The whimbrel is a smaller edition, and one that trips people up every spring passage. Look for a shorter, slightly stouter decurved bill and a strongly striped head — dark crown lines with a dark stripe through the eye. Its flight is snappier and more buoyant than a curlew's, and it often gathers in small, tight groups on wet pasture behind the sea wall. The voice settles it: a rapid rippling series of piping whistles, often counted as seven notes, which has earned it the old name of "seven whistler". A curlew sings one long idea; the whimbrel rattles out a tittering sequence and moves on.

Godwits: Straight Bills, Bold Tails

Both godwits fly with a straight bill and a distinctive tail-heavy look, but their flights differ in detail. The black-tailed godwit is the larger and rangier of the two, with very long legs that project clearly beyond the tail, and a bill that often shows a slight upward kink near the tip. In flight it displays a bold white wingbar and a black tail band. In summer it glows orange-rufous across the head and breast; in winter it is a pale grey-buff bird that looks, at a glance, much like its relative. Its call is a loud, almost indignant wicka-wicka-wicka.

The bar-tailed godwit is stockier, with shorter legs that barely pass the tail tip. In flight, look for a white rump and a finely barred tail, but no strong white wingbar. Winter birds are grey-brown above and pale below; in summer the underparts turn deep brick-red. The call is shorter and more nasal — a clipped kvyk or kirrik, given singly or doubled, with none of the black-tailed's tripping rhythm.

Redshank: The Voice That Gives the Game Away

Redshank are the sentinels of the marsh. Medium-sized, grey-brown above and pale below, they fly on fast, flickering wingbeats and show a bright white trailing edge to the wing and a white wedge up the back — the single best clue when the legs are out of sight. The legs themselves are a rich orange-red, but at distance they disappear in the mud. Fortunately, redshank rarely stay silent. The alarm is a ringing, piping teu-teu-teu, clear and carrying, and a single upslurred tuee often precedes the flushing of an entire roost.

A Quick Field Comparison

• Large, very long curved bill, slow flight, mournful "cur-lee": curlew.
• Smaller, striped head, rapid seven-note whistle, spring passage: whimbrel.
• Long straight bill, legs past tail, white wingbar, "wicka-wicka": black-tailed godwit.
• Shorter legs, white rump and barred tail, nasal "kvyk": bar-tailed godwit.
• Fast flight, white trailing edge, piping "teu-teu": redshank.

Fieldcraft: Light, Tide and Listening

The best silhouettes come at dawn and dusk, when birds stand against a bright sky or a silver estuary. Pick a vantage point with the light behind the flock and use a roost on the rising tide: as water pushes birds up the mud, calls intensify and identification becomes a matter of sorting voices rather than squinting at plumage. A breeze blowing from the birds towards you carries sound; if the wind is on your back, you will hear far less.

Spend your first hour simply listening. Note the rhythm of each call — single, doubled or rippling — and record a few on your phone for comparison at home. Keep a note of the date, too: whimbrel are mainly passage birds in late April and May and again from July to September, whilst curlew and redshank hold territory and roosts all year. Once you can name a bird before you lift your binoculars, you have learned the estuary's shorthand.