大象传媒

NEW TECHNOLOGY CREATES OLD HABITAT

On the wing - Will the birds take to the new salt marshes?

The Exe Estuary has been a traditional stopping point for migratory birds, but man's influence on the environment has put these breeding grounds under threat.

Now the Royal Society for the Protection of Birds (RSPB) is sculpting the landscape in a different way, in an attempt to preserve the fragile ecosystem.

Environmental pressures

Over 100 hectares of salt marsh and 150 hectares of open mud flats disappear every year in the UK.

Agriculture, rising sea levels and dredging of estuaries all play their part in displacing this natural resource.

The RSPB is aiming to turn the tide of this destruction by returning Goosemoor, six hectares of pasture land at the head of the Exe Estuary, to its original state as an intertidal habitat.

Such a habitat has not been found on this part of the River Exe since the 1840s.

The site is right next door to an existing wildlife reserve - the RSPB's Bowling Green Reserve, the main high tide roost for the north of the estuary.

Sea wall

Sunset on the Exe - but the future now looks bright for the wildlife

However returning this new land to salt marshes and mud flats is a tricky engineering feat.

The site was reclaimed as pasture land in the 19th Century.

A sea wall was built to stop the estuary tides from flooding the land and destroying the grazing.

To return it to its former state would normally involve the demolition of the sea wall, and then nature would take its course and the tide would flood the site.

However, the RSPB must be mindful of areas around their site. Simply demolishing the wall would not just flood their land but also wash away the railway line that runs alongside it.

Managed solution

Letting it all flood in - the new tide gate in action

Instead the RSPB has installed a tide gate.

The tide gate is like a giant toilet cistern - it allows the water to rise so far, and then shuts off the supply.

This way, when enough water is in the new reserve, the gate automatically closes so no more can come flooding in.

The land is therefore spared the effects of very high tides and the surrounding lands are not threatened with flooding.

The tide gate also allows the tidal waters to drain out of the site once the estuary tide is in retreat. This leaves the reserve to follow the lead of nature.

The tide gate has been up and running for four months now.

The RSPB are still experimenting with how much tidal water they should allow to pass through their gate to create the habitat they want.

The monitoring is proving crucial. The RSPB must ensure that the water in no way threatens the adjacent railway line.

They also need to make sure that they don't flood the whole of the land.

They need to leave patches of ground that will remain dry throughout the day and throughout the year.

These dry areas will be needed if the new site is going to become a breeding ground for birds as well as a stopover place for migrants.

The nest sites need to be protected from the tides if chicks are not to be washed away.

The tides of change

Tasty snacks to be had, as flora and fauna colonise the area

It will take time for this new site to transform into a saline habitat that supports the type of vegetation and invertebrates that the estuary birds will feed on.

Volunteers are monitoring the flora and fauna of the new site to see how quickly it is being colonised by marshland species.

They are also carefully monitoring the salinity of the area.

One of the birds the RSPB is hoping will make a home there is the avocet.

They already spend the winter on the Exe, but the RSPB wants them to stay and breed along with other waders like redshank.

The avocet bird demands a salty environment, and the volunteers are doing all they can to make sure they can achieve the particular levels of salinity this fussy bird requires.

If they do get the avocets to move in, the estuary would become the most westerly habitat in the UK that the birds visit.

The future

"We're quite optimistic about Lapwing actually breeding here next summer."

RSPB

At the moment the area's birds are mostly sticking with the RSPB's neighbouring Bowling Green reserve.

The salt marsh ecosystem in the new reserve needs time to fully establish itself.

However, observers are starting to notice increasing numbers of birds coming to the new site for a quick look around.

The RSPB is confident that by the summer they will see birds moving in with their families, and the first Goosemoor chicks take to the air.

It is also hoping that the tide gate technology can be used elsewhere in the country to preserve other tidal habitats.