The High Tide at Parkgate is something special: a show that is a marvel of time and space, a natural spectacle that draws hundreds of birders and other enthusiasts to the village to watch it unfold every time it happens. Each show is different, and regulars return time and again, drawn by the thrill and unpredictability of what might unfold. This isn’t the normal tide, this is the perigean spring tide which occurs only six-eight times a year.
A primer on tides
The tide is the rise and fall of the surface of the sea caused by the gravitational pull of the moon as it passes above the earth. Around the times of a full moon and a new moon, the moon and the sun are aligned, which increases the gravitational effect and increases the range of the tide – the distance the water rises and falls between high and low tide. This is what is called a spring tide, and it is nothing to do with the season.
The effect is heightened when a spring tide coincides with the moon being at its closest distance to the earth, known scientifically as the perigee. A perigean spring tide is the highest of the highs – up to a foot higher than other high tides.
Other factors which affect the height of the tide are atmospheric pressure and the state of the wind. High pressure means there is more air above our heads, and the total weight of all that air pushing down on the surface of the sea subtly suppresses the rise of the tide. Conversely, low pressure allows the tide to rise more freely.
Parkgate is on the Dee Estuary, which opens out on the Irish Sea in a broadly north-westerly direction. This means that a stiff north-westerly breeze literally pushes sea water along towards the mouth of the estuary until it hits a barrier – the underlying sea floor and ultimately dry land. When it reaches the barrier the water can only go in one direction, upwards; hence, when there is more water coming in, the tide rises more than it would otherwise.
Parkgate Marshes
Situated on the Wirral, Parkgate was originally a small fishing village and port. Up until the early 1800s it was also the main port on the route between London and Dublin. However, in the mid-19th Century, the river began to silt up, making it difficult for ships to access the port. The silting up continues to this day and if you have visited Parkgate you know its sandy beaches are long gone, and the quayside is incongruously positioned far from the open sea.
The space between the village and the open channel of the River Dee is known as Parkgate Marshes. Part of the larger Dee Estuary Special Protection Area (SPA) and Site of Special Scientific Interest (SSSI), it covers an area of around 280 hectares (700 acres) and consists of intertidal mudflats, salt marshes, freshwater pools, and reedbeds.
You can’t really call it land because it isn’t solid ground. Much of it is porous mud, which means it quickly absorbs water when the tide comes in, and when it rains. Patches of the visible surface of the marsh are essentially mats – swathes of vegetation with their roots entangled and bound together by mud – that lie unanchored on top of more solid ground, or float freely on the water. When the tide comes in these mats can become floating, moving islets.
The Dee Estuary SPA itself is a site of international importance for birdlife, extending to around 16,000 hectares in total and home to an incredibly diverse range of bird species, with over 120 species having been recorded. It is particularly important for wading birds, which feed on the rich mudflats and salt marshes at low tide. Among the species that can be seen on the estuary are oystercatcher, curlew, redshank, dunlin, black-tailed godwit and knot. The estuary is also home to a significant population of wildfowl, including pintail, wigeon, teal, and shelduck.
Importance
It is also a particularly important site for migratory birds, which use the area as a stopover during their long journeys between breeding and wintering grounds. During the Autumn and Winter months, the estuary is home to large numbers of birds that have migrated from their breeding grounds in northern Europe and Scandinavia. These include pink-footed and barnacle geese, whooper swan, and a number of duck species.
Many of these species are rare or endangered, and the area is considered one of the most important bird-watching sites in the UK.
In addition to its importance for breeding and migratory birds, the Dee Estuary SPA is also home to a range of other wildlife, including mammals such as otter and water vole, and a variety of invertebrates such as butterflies and dragonflies. The site is an important area for research and monitoring, and is managed by a range of conservation organizations, including the Royal Society for the Protection of Birds (RSPB).
Action
To recap, we have a large expanse of habitat teeming with diverse wildlife, and a huge volume of water bearing down on it as the tide comes in. At every high tide the incoming water sweeps across the exposed mud flats on each side of the river channel. It flows into the open channels at the far edge of the marsh, filling them with water.
The birds feeding on the mud and in the channels are displaced and have to move to safer, higher and drier ground to sit out the tide. This is normal – they do it at every incoming tide and it is part of their routine to have a rest, to roost – except on a spring tide, when the water keeps rising, moving further inwards, creeping ever higher.
When the water reaches the top of the channel it spills out onto the surrounding vegetation, displacing not only the birds, who have to move again, and again, but also the small mammals and invertebrates hanging out there. This is open season for their predators, both larger mammals like foxes, and birds such as crows, herring gulls and raptors.
All this activity provides the human spectator, ensconced on dry land, with an on-going spectacle. To begin with only the committed birders armed with the best binoculars, or better still a spotting scope, get to see much of the action. Birders are generally a friendly bunch and there is a lot of calling out so that others can keep up with what is going on. “Flock of knot coming in from the right”; “pintail just landed on the lagoon”; “was that a wheatear that just went past?”
The tumult and frenzy grow from a standing start about 1-1¼ hours before high tide to a climax just a few minutes before the tide turns.
Swarms of gulls flying around in seemingly random patterns calling out the familiar gull cries.
Flocks of waders coming in from the mudflats, settling first of all at the far edge of the marsh only to be moved on a few minutes later by the encroaching tide.
Other waders, ducks and larger birds such as herons exposed to view as water fills their channels and they fly off to find a more secure place to feed.
Groups of small birds that normally feed on insects and seeds in the vegetation are disturbed by the activity around them, take off seemingly in confusion, fly a short distance, land, only to repeat the exercise in quick succession.
Predators focus their highly tuned senses looking out for prey – the mice, voles and shrews they feed on, disturbed by the rising water, risk being forced out into the open. Short-eared owls and marsh harriers quarter the scene below them; kestrels hang in the air, their bodies performing exquisite three dimensional acrobatics to keep their heads perfectly still.
Opportunist feeders such as carrion crows and herring gulls watch, waiting for the moment to try their luck.
The landscape of the marsh is also changing. The first thing the observer sees is the far edge of green/brown vegetation giving way to a shimmering, shifting intrusion which is the water. The sea doesn’t come in uniformly like it does on a flat beach. It comes up the channels, penetrating ever further, hiding more and more of the vegetation under its surface.
Things quieten down even more quickly as the wildlife comes to terms with its new temporary surroundings. Then, as the waters recede, things gradually return to normality – a slightly different normality to boot. New driftwood, flotsam and jetsam have been deposited. Some of the mats and the existing detritus brought in by a previous high tide have moved or disappeared. It’s still the same old marsh, just a little retouched you might say.
The onlookers frequent the shops, cafes and pubs before piling into their cars to go home.
In 12 hours’ time the cycle will repeat, but with less excitement, little drama and few onlookers. Until the next High Tide!
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