Why the Tide Matters More Than Any Other Factor

On an estuary, the tide is not scenery. It is the thing that decides where every bird is, and when. The same stretch of mud that looks empty at ten in the morning can be seething with waders by two, and the same roost bank that holds three thousand knot at high water will be bare shingle six hours later. If you plan a trip around the birds alone, you will spend a lot of time looking at nothing. Plan around the water and you will find them almost every time.

Estuaries are tidal rivers, and the water moves fast — often at walking pace, sometimes much quicker. As it advances, birds are pushed off the mudflats and funnelled into a shrinking area. As it retreats, they follow the waterline back out, spreading across the flats. Understanding that rhythm is the difference between a frustrating morning and a memorable one.

Reading a Tide Table Before You Set Off

Tide tables give you two numbers that matter: the time of high and low water, and the height in metres. The height is the one people ignore, and it is often the more important.

• Range tells you how far the water will move. A high water of 5.2 metres means water pushing high up the saltmarsh and covering most of the mud. A 2.4 metre high water may barely touch the lower flats.
• Spring tides, falling a day or two after a new or full moon, are the biggest. They push birds off nearly everything and concentrate them into the few remaining roosts.
• Neap tides, around the quarter moons, leave large areas of mud exposed even at high water. Roosts may not form at all, and birds stay spread out.
• Local weather shifts the real thing. A strong onshore wind and low pressure can lift the actual water level half a metre or more above the prediction; high pressure and an offshore breeze do the opposite.

Check the table the night before, then look at the wind forecast and adjust. Allow half an hour either side of any predicted time — estuaries rarely run to the minute.

High Water: Roosts, Flocks and Counting

High water is the classic estuary spectacle. Waders that have been scattered across square miles of mud are compressed onto a handful of islands, spits, old jetties and saltmarsh edges. You may find mixed flocks of dunlin, knot, black-tailed godwit, curlew and oystercatcher, often with shelduck and gulls alongside them, standing shoulder to shoulder.

These roosts are not casual gatherings. Birds are conserving energy, digesting, and waiting for the flats to reopen. That makes them vulnerable. A single careless approach, or a loose dog, will lift the whole flock and cost them energy they cannot easily replace, particularly in cold weather.

So watch from a distance. Set up a scope on the highest ground you can reach, well back from the roost, and let the birds come to you. A flock that settles, preens and dozes is a flock that has accepted your presence — that is the signal you have positioned yourself correctly.

The Rising Tide: The Best Window of the Day

If you only take one tip from this article, take this one. The two hours before high water on a decent spring tide is the finest birdwatching an estuary offers.

As the water creeps across the flats, feeding waders are pushed closer and closer to the shore, and they feed hard in front of the advancing edge. Curlew probe the softening mud, dunlin and ringed plover pick along the waterline, avocets sweep their bills side to side in the shallows, and everything drifts gradually towards you. You get the intensity of a roost with the activity of a feeding flock, at a range you can actually enjoy.

The falling tide is the mirror image, but less useful: birds follow the water away from you, so the flock disperses and recedes as you watch.

Low Water: Vast Flats and Patient Fieldcraft

At low water the estuary is at its most expansive and its most difficult. Birds spread out across enormous areas of mud, and many will be hundreds of metres away, feeding in channels and pools you cannot see into. It is a wonderful time for watching behaviour through a scope, and for picking out scarcer species among the common ones, but it demands patience.

Use it to learn the site. Note where birds gather as the water begins to return — those are the feeding areas that will be worth watching on your next visit, and they tell you where to position yourself before the tide turns.

Staying Safe and Treading Lightly

• Never walk out onto the mud. Estuary mud is soft, deep and cut by channels that fill quickly from behind. On big estuaries the incoming tide can outrun a walking person.
• Give roosts a wide berth, and keep dogs on a short lead near the water at all times.
• Stay on marked paths and sea walls, especially where saltmarsh and shingle provide nesting habitat in spring and summer.
• Respect closed areas — many estuaries protect sensitive roost sites, and a small detour costs you nothing.
• Carry a tide table and know your exit route. If a channel is between you and the car, do not gamble on it being shallow.

Get the tide right and an estuary gives you one of the great wildlife spectacles of the British coast. Get it wrong and you will simply wonder where all the birds have gone. Now you know.