Wetland wildlife is booming at Ouse Fen, thanks to 30-year vision of RSPB and Hanson UK
Walk through RSPB Ouse Fen in the spring or early summer and an extraordinary booming sound may greet you.
Bitterns are Britain’s loudest bird, with a unique and unmistakable call that carries 5km and measures around 100dB – which is comparable to a helicopter hovering at 100ft, or a train.
And it’s a very welcome sound, for it reflects that the bittern population is, well, booming, having reached critical levels in the 1990s.
Just 11 males were recorded in the whole of the UK in 1997.
But a concerted effort by the RSPB based on scientific research into the species’ needs has brought them back from the brink and in 2021 there were a record-breaking 228 ‘boomers’ recorded in the country.
Thanks to a groundbreaking partnership working between the RSPB and Hanson UK to restore the enormous Needingworth quarry, a good number of these enigmatic birds can be found at Ouse Fen.
“Our record count is 12, which is something like five per cent of the UK population and more than there would have been in the whole of the UK when this project started,” RSPB site manager Chris Hudson tells the Cambridge Independent.
“It’s been a massive success and it demonstrates how projects like this can make a huge difference.”
An exemplar of landscape-scale conservation, together, the RSPB and Hanson are recreating some of that lost wetland habitat that once dominated the wild fenland landscape before it was drained for agriculture.
Planning began back in the 1990s before work began in 2001 – and the numbers involved are staggering.
More than 28 million tonnes of sand and gravel are being excavated at the quarry in sections, which are progressively restored by Hanson before they are handed over to the RSPB for management.
The site will stretch to more than 700 hectares or 980 football pitches in size by 2030.
And when complete, the reedbed at its heart will be Europe’s largest at 460 hectares (644 football pitches).
“We are 20 years into a 30-year project, so it’s really long-term,” continues Chris. “We will be going at least until 2030 and there’s a small chance it could go on longer if possible extensions come about.
“We’ve created about 150 hectares of wetland in a three square kilometre nature reserve and there is a big part of the project that is semi-restored. In various stages, we are about two-thirds around this gigantic site.”
Chris works closely with Dave Southgate, Hanson UK’s principal landscape architect, to create a mosaic of wetland habitats that benefit wildlife.
“In the bad old days of quarrying, they would dig out pits and leave them,” says Dave.
“This had to be planned from the start, showing a scheme of working and progressive restoration.”
First, Hanson – which supplies heavy building materials to the construction industry – removes a one or two-metre layer of soil, or ‘overburden’, that lies on the gravel it wants to extract. The gravel might stretch to four metres deep.
The overburden is moved once and then, once quarrying is complete, moved back to restore the landform, now several metres lower.
“Stage by stage, as we go around the site, we strip overburdens and soils and put them back into the restored landform. There are no big voids of worked-out quarry left,” explains Dave.
“I do detailed drawings of the landforms that fit the overall concept and masterplan and pass them to the RSPB for approval.
“The final soils in that area are very peaty because it was originally reedbed fen, which is what we are restoring it to.
“Originally it would have been wetlands at the original ground level and now we’re restoring it at a lower level – a few metres down because the gravel has gone, but roughly to the same thing that existed before.
“Mostly it was too wet even for wet woodland, so you would have got a lot of natural fen. Historic drainage came in to turn into farmable land, but we’re reversing that, in effect.”
Restoring such land to a natural wetland state, rather than deploying it for agriculture, is helping to trap carbon.
“A positive of what we’re doing is taking out intensive farming, which keeps turning it every year, making the peat oxidise in the air, and CO2 is released. But by putting it into a wetland, it is basically pickled and doesn’t rot and give off C02. So we’re doing a positive job in sequestration,” notes Dave.
Chris adds: “We are doing some work with the Centre for Ecology and Hydrology to get some scientific data gathered to show that is happening. We have some research equipment on site.
“We need to show the maths, as it’s so little researched, but in principle as soon as you stop farming and turn something into a nature reserve, there’s a very strong likelihood that you are sequestering carbon.”
Dave notes: “The locals in the area will be familiar with peat shrinkage from the posts that are in the ground.
“The ground levels are lower because once you take the water away, the peat isn’t preserved, it oxidises and shrinks. A lot of the road problems exist in that area because of that.”
Sitting between five villages, the reserve has been carefully planned to create the type and variety of habitats in which wildlife can thrive.
“The detailed plans show different levels of landforms. You can have deep water, or shallow water with reeds, drier fen… the different levels create different habitats that the RSPB ask me to build in, so that when we do flood it, you have the right landform and hydrology levels for certain habitats,” explains Dave.
Natural regeneration is now in effect, but that was not always the case.
“It’s much, much easier to get a reedbed started than it used to be,” recalls Chris. “In the first 10 years, between the RSPB and Hanson, we planted about 130,000 reeds. But the reality is we’ve virtually stopped that now. There’s such a gigantic seed source available now in the water and the air, so it is regenerating all on its own.
“Dave and I swap drawings to create these range of habitat types and build in lots of ‘edge’, as wildlife congregates and gathers on all these edges, especially our key species – bittern, which are known to spend most of their life within 15 metres of a ditch edge.
“Once Dave and Hanson’s team have created the landform during the summer months, they are flooded. Hanson builds in sets of water control structures to allow us to bring in water and get it out again, which is just as important.
“We bring it to a relatively low level to start. Ironically, so we don’t bring in so many birds that they graze all the reed away. We raise the water level very slowly and natural regeneration takes over.
“The only other thing we really do to kickstart the whole process is possibly introduce fish. That is five or 10 years down the line.
“So it’s a really simple process. Without doing any disservice to Hanson, or ourselves, nature is doing most of the work.”
Dave adds: “Giving it the right landform and the right depth of water is key. Sometimes we don’t want reed to take up, so we produce water that is more than two metres deep. It doesn’t really grow out into that. So you can design in self-management and we stair it through the right landforms.
“We do it cell by cell and we are now handing back totally finished cells, with inlets put in so the RSPB can manage the habitats.”
Ten cells, of varying sizes, are complete, and a similar number are to come.
But where is all the water coming from?
“As Hanson are quarrying the site, they need to keep it dry to do their work, so they need to dewater it. They lead it to a very deep drain and that is pumped up to a settlement lagoon. And that is the source that we’re using,” says Chris.
“We are close to where we are going to exceed the supply available so, between Dave and his colleagues and mine, we are working on a project to create some abstraction infrastructure to lead water from the river.
“We could take 2.73 million cubic metres in the end. But we’ll take it in stages and see how much we need. Potentially, a huge volume of water will be abstracted using syphons.”
The word ‘abstraction’ is enough to set alarm bells ringing in the Cambridge region, where water companies have been criticised for taking water from the chalk aquifer.
Chris explains the scenario is very different for this Ouse Valley project.
“It’s been designed to only operate during major floods. I can’t say we’ll be helping in a very significant way to reduce floods, but there will be some effect,” he says, adding: “We won’t be taking in dry conditions. The licence managed by the Environment Agency would not permit us to do that.”
The effect of this wetland recreation on wildlife has been remarkable – and Chris still remembers the day the first bittern was seen on site in May 2011, only seven years after the first reeds were planted.
Perhaps surprisingly, it was not the booming of a male that revealed that nesting was taking place.
“A couple of volunteers on the site rang me to say there was a female flying backwards and forwards over the top of them, which is always a sure sign of a nest. That was the spark that started it all.
“It was in advance of a male bird being seen. We don’t know where the boomer was,” says Chris.
Brown, black and white in colour, bitterns are members of the heron family and spend their time moving through reeds at the water’s edge, searching for fish. They became extinct as a breeding bird in the late 19th century due to wetland drainage and hunting, but were recorded as breeding in Norfolk in 1911. Gradually, they recolonised, with about 80 booming males present by 1954, only for their numbers to collapse again as their reedbed habitats became drier through lack of management.
Thankfully, that has changed again and by 2030 the RSPB hopes to have 20 booming males at Ouse Fen.
And while they are generally easier to hear than see, other key wetland species are more conspicuous on the reserve, notably marsh harriers, which have also benefited greatly from conservation efforts across the country, and particularly in East Anglia.
“We regularly get six marsh harrier nests a year and there are about 300-500 marsh harriers in the UK now. In the 1970s, there was one, so that’s another big success story,” says Chris.
You may also hear the distinctive pinging on site of bearded tits – or bearded reedlings, as they are also known, since these attractive little reedbed birds are not actually members of the tit family.
The RSPB hopes to have 100 pairs nesting by 2030, which would represent 25 per cent of the UK’s entire population at it was in 2000.
“We’ve also got otter, water vole and 22 species of dragonfly,” adds Chris. The Norfolk hawker is the latest of those dragonfly species to take up residence.
“And we are being colonised by common crane now. We regularly have a pair of them,” he continues.
“We had the first breeding cattle egrets in Cambridgeshire two years ago on the reserve. We think we may get other new colonising species moving in. We are keeping our eyes peeled.”
Botanists, meanwhile, have discovered what is thought to be the largest population of nodding bur-marigold in the county – a species thought to be present at only seven sites in the entire fenland area.
It is, undeniably, a terrific success story, and a blueprint for how conservationists can work in tandem with the minerals industry to create valuable wildlife habitat.
“We know we can replicate this elsewhere and we are very keen to do that, and find other organisations and opportunities to do something similar elsewhere in the country,” says Chris.
The RSPB has had similar success at restoring Ham Wall, a former peat extraction site in Somerset, while Hanson UK worked with the charity at its Middleton Hall site in Tamworth.
“The Wildlife Trust has also taken on our sites,” notes Dave. “There is one near Derby at Repton and that is now Willington Wetlands, where there are breeding beavers.
“They all contribute to nature conservation and public access.”
That access at Ouse Fen will eventually includes 32km of new public rights of way.
“Hanson has put in significant numbers of them already, with more to follow as the reserve grows, including cycleways, bridleways, public footpaths and our own trails,” says Chris.
A new car park, that can be sustainably managed for years to come, enables nature-loving visitors on the site, although there are no plans for any more major visitor facilities at this stage.
“Ouse Fen has very simple facilities, and that’s probably not going to change too much, although we may be able to provide some improvements,” says Chris.
“However, our sister reserve at Fen Drayton, a few fields away from the southern edge of Ouse Fen, lends itself to visitor development to a greater degree and we are putting together plans for a significant new vision for visitors down there.
“Fen Drayton is more accessible because it’s on the guided busway, with a Sustrans route through the middle of it and it’s a little closer to Cambridge. That is the entry point to the Ouse Valley.
“Ouse Fen and Ouse Washes are a bit more distant, but if you are more adventurous or more focused on bird watching you might head there.”
Indeed you might. With booming bitterns, sky-dancing marsh harriers and pinging bearded tits amid a gloriously wild landscape, there are good reasons to visit.
