AFTER a long day at work Matt Prior has another important engagement - with a population of tree sparrows.

Between April and August, the man responsible for a local resurgence in the numbers of this modest, brown bird spends about 30 hours a week, on top of the responsibilities of his job at Thames Water, supporting and recording the tree sparrow population.

To say he is a man with a mission seems an understatement: since 1999 he has devoted himself to the project, setting up nesting boxes, working with farmers, ringing and recording birds and gathering a vast amount of data and knowledge.

In the north Wiltshire area he covers, Matt reckons there were 30 to 40 pairs when he started – and now, 18 years later, around 500 pairs.

“People call me the bird man,” he grins. That hardly seems a surprise.

Matt has invited me to join him at the beginning of another long session, checking bird boxes and ringing the tree sparrow chicks. We start on a farm at Berwick Bassett. On the slight elevation of the downs, the cow parsley is still blooming in long, white lines at the borders of the field.

The trees and fields are lushly green under a cool, grey sky. Matt is cheerful and energetic, tuned in to his surroundings and alert to the movement of every passing bird, and the sound of each song they make.

“That’s a corn bunting,” he says, pointing to a bird on a fence post. “That’s a female. She’ll have a nest down there. And there’ll be a male somewhere, watching over her. Look there he is!”

I see another bird perched on the telegraph wire high up. Matt identifies a wren flying past, before I have a chance to recognise its distinctive perching shape, and then the song of a yellowhammer. He seems tuned in to a different frequency, a complex world full of the on-going life dramas of numerous birds. He says the songs indicate what the birds are doing – guarding territory, offering a warning, courting a mate.

“It’s all like a story book to me,” he says. “It’s all going on around us.”

It is the tree sparrow that has become Matt’s particular fascination. Smaller than the house sparrow, it has a chestnut head and nape, rather than grey, with white cheeks and collar and a black cheek spot. They are shyer than house sparrows, and particularly wary of cats, Matt says.

Between 1970 and 2008, the population suffered a precipitous decline, estimated at 93 per cent.

“They’ve gone from Hampshire, Dorset, Devon, Cornwall and Berkshire,” Matt says. “They have all disappeared.”

Matt, who lives in north Swindon, started bird-watching in his twenties and joined the Wiltshire Ornithological Society in 1994. Two years later, he became their conservation officer, which had him wondering what he might do.

“I thought, what could I help with? I knew tree sparrows had declined, and I knew they used nesting boxes and would feed from feeders, so I thought I could help them,” he explains.

While the reasons for the almost disappearance of the tree sparrow are uncertain, Matt has plenty of ideas.

“A long time ago they adapted to live with human farming,” he says. “But farming has changed a lot in the last 50 years, and it’s changed to quickly for them.”

The populations of elm trees with their nooks and crannies perfect for nesting have largely disappeared, and a system of harvesting by hand that left grains of wheat on the ground has been replaced by an efficient mechanised system which leaves no gleanings for seed-eating birds.

“Tree sparrows eat seeds during the winter, and insects during the summer,” Matt says.

He is working with farmers to provide large feeders for tree sparrows, full of wheat, barley, millet and even quinoa. The food is available to the birds in the summer too, to support the diet of the parent birds in case of bad weather, when insects are harder to come by. Over the years of his tree sparrow project, Matt has put up 1168 individually numbered nesting boxes at locations all around north Wiltshire. During the breeding season, from April to August, during which time tree sparrows might have three broods of up to six chicks, he dedicates hours every day to visiting the boxes, keeping detailed record of the chicks and fitting a numbered ring onto the chick’s leg so he can collect accurate data about the birds as they become adults and start breeding.

“I do it when they are small enough to handle, but big enough to survive, which is ideally at eight days,” he says. “They fledge at about 14 days.”

They readily take to nesting in the wooden boxes Matt has made and they create nests from dry grass and feathers. Matt has observed they put a single hawthorn leaf into the next and speculates that when the leaf has dried out, it signals to the bird the humidity in the next is right for laying eggs.

Occasionally people steal the nest boxes – and astonishingly, some still collect the eggs of these endangered birds – but Matt said many people were fascinated by his project, volunteered to help and followed him on Twitter.

He also paid tribute to the farmers who helped the project and worked hard to protect the environment that was also a livelihood for them. One very supportive farmer (and talented wildlife photographer) is David White, of Manor Farm, who dedicates strips of land amounting to 70 acres to growing seed and cereal plants which are not harvested but left for birds to eat. Nest boxes and feeders set up on his land allow the tree sparrows to flourish.

He has also set aside an area of grassland on the downs where the grass is left to grow to encourage small mammals such as mice and voles, which feed birds of prey such as kestrels, kites, buzzards, owls, merlins and sparrowhawks.

“Matt is absolutely brilliant,” David said. “He never stops. We need the endless enthusiasm of someone like Matt. We are really fortunate to have him here.”

Many farmers in north Wiltshire are members of The Marlborough Downs: A Space For Nature – working together to promote wildlife and the natural environment. They have an open day at Temple Farm on Sunday June 10, which Matt will be attending.

“I love the fact I can inspire or educate others,” he said. “It used to be just me and the birds, but now I appreciate sharing what I know.”

For more information on A Space for Nature and the farm open day, visit the group’s Facebook page. Follow Matt on Twitter @mattthesparrow.