IN his camouflaged jacket and woolly hat, and with a fine pair of binoculars round his neck, Mark Mead is marching eagerly across the swathe of grassland that stretches for miles, across to the chemical complexes of industrial Teesside.

His wife Cilla is close behind, just about managing to keep up. They’ve been together for 32 years, running restaurants in north London, but it’s a love of birds which has brought them scurrying to this fascinating part of the North-East.

Well, it was Mark’s passion first but Cilla was quickly conditioned into the world of ornithology, and now they’re on a 22-day holiday dedicated to spotting as many birds as possible.

They started up the west coast, taking in Blackpool and Carlisle, before heading to the Isle of Mull and the Cairngorms. Now, they’re working their way down the east coast and were staying in Northumberland when the digital grapevine buzzed with news that the RSPB Saltholme Nature Reserve, near Seaton Carew, had rare visitors.

Most notably, two whiskered terns have arrived from Eastern Europe – blown across the North Sea by the north-easterly air-flow that makes this region such fertile territory for bird-lovers. There’s no shortage of common terns here but the whiskered variety warrant a special mention in the Saltholme records. It’s a tern up for the books.

“It’s very exciting. They shouldn’t be here - they’re here by mistake,” says Mark, keen to get to the blue-doored wooden structure known as “Paddy’s Pool Hide”, so he can train his “bins” on the man-made lake in the hope of glimpsing the stars of the show.

Adam Jones, Saltholme’s friendly assistant warden, explains that there’s not that much difference between the whiskered tern and the common tern. The common variety has a black tip on its red bill, whereas the whiskered wonder has an all-red bill and a darker grey belly.

But it’s enough of a difference to give the whiskered tern celebrity status and bring “birders” – I’m warned not to call them “twitchers” – flocking from far afield. There’s also been a report that a great reed warbler’s come to Saltholme. They only come to Britain in very small numbers every year and they live in reed beds so they’re usually only ever heard and not seen. Just the sound is exciting enough for the birders.

Due to the internet, intelligence about rare sightings spreads quickly among the bird-watching community. “The technology has made a huge difference,” says Adam.

Mark and Cilla have chatted long enough – this is their holiday, they’ve got birds to see, and they’re taking big steps through the grass again.

It’s eight years since the magnificent RSPB centre was built on the site of Saltholme Farm and around 90,000 people visited last year. The society had signed a 99-year lease on the site the year earlier, having formed a partnership with the Teesside Environmental Trust which acquired the land in 2004.

The “Saltholme Pools” have a history going back centuries, to ancient salt mining by monks, but the water-filled craters were only designated as a Site of Special Scientific Interest in 1999. It’s an evolving story which has enriched the area, with Saltholme adopting the slogan: “Giving nature a home.”

Since Saltholme opened, a new lake has been created, with its own island, where the seabirds are making a right racket and belligerently competing for a space to call their own. It’s intriguing to discover that they pack themselves onto the island as tightly as possible as a defence strategy against predators such as lesser black-headed gulls. If one of those dive-bombers tries to attack any chicks, the terns will flock around it and “poo” on it from a height. Charming.

“It’s the most exciting time of year,” says Adam, who confesses to having landed his dream job. “It’s peak migration time so it’s all happening. There’s life all around us.”

Saltholme already has birds that have come to breed here - species like garganey, reed warblers, and the sand martins which have had their own special sandbank built close to the visitor centre for easy viewing. Other birds, including redshank, grey plover, and the black-tailed godwit, are on their way to breed in the Arctic, Russia, Iceland and as far away as Canada.

“Saltholme is like a huge airport lounge,” explains Adam. “They’ve done the main flight from Africa and they land here for a rest and a bite to eat before setting off for their breeding grounds. The North-East is a fantastic place to see birds because the easterly winds blow them across the North Sea and it makes this the perfect stopping off point. We’re so lucky.”

And it’s heartening to hear how industry and nature are working side by side, with the likes of petrochemicals company Sabic supplying water to support the new wet grassland area that is teeming with the insects that the birds love to eat.

“We’ve had a lot of help from industry and that’s really important,” says Adam. “Our aim is to keep the site developing, helping the habitats to mature and it’s about working together to do that.”

One priority is to build up the numbers of lapwings, which have been in decline in Britain in recent years.

Meanwhile, Mark and Cilla Mead, 32 years married, emerge from Paddy’s Pool Hide with satisfied smiles. The diversion to the wet grasslands of Teesside has been well worth it for the pair of holidaying love-birds.