Eileen Shields can still remember her first trip out to see the Bass Rock, home to more than 150,000 gannets and guillemots.

There had been a queue at North Berwick harbour, she recalls.

Eileen said goodbye to her husband Kevin and promised to see him back on shore in an hour.

She was on her way to hear the bird calls echo off the 320-million-year-old rock, its lower ledges strewn with feathers still damp from the sea, while seals hauled their heavy bodies up to rest on the rocks below.

It was going to be one of those delightful moments wildlife lovers live for.

Then, without quite realising it, Eileen jumped aboard the wrong boat.

"I did think it a bit odd when we seemed to be going in the opposite direction," she says.

But not quite so odd as when she finally landed on the rocky shores of an altogether different island and was promptly handed a pair of shears.

"That was a wee bit strange, I'll admit," says Eileen with a chuckle.

"Then they told me that I'd ended up with the SOS Puffin Project."

It was, 60-year-old Eileen will say to anyone who asks, the best mistake she has ever made.

Today, Eileen is one of 1000 volunteers who has dedicated the last decade to restoring the numbers of one of Scotland's most iconic sea birds.

Ten years ago Scotland's puffins were in crisis.

Out on the islands in the Firth of Forth, the little bright beaked birds had crashed from 28,000 pairs to barely a few thousand, leaving what had once been one of the UK's largest puffin colonies in a desperate state.

Nicknamed the 'clowns of the sea' for their strikingly coloured faces, they had fallen victim to an alien invasion.

"The problem was a giant plant called tree mallow which grows to about three metres in height," says John Hunt, who co-ordinates the SOS Puffin project.

"It had grown into a tangled jungle that we couldn't crawl through, let alone the puffins."

With its large velvety leaves and antiseptic properties, the tree mallow had been used as bandages in medieval times and 300 years ago, soldiers manning the Bass Rock fortress began planting it for medicinal use.

Unfortunately, the fast-growing plant didn't stay contained there and soon spread rapidly to the nearby islands of Craigleith and Fidra.

By 2007, the root covered 90 percent of the islands, tangling up the burrows where the puffins had nested and leaving no safe space for further little pufflings to hatch.

"It was then that people really looked up and spotted the problem," says John.

But by then, the puffin numbers were frighteningly low.

"The seabird centre acted as a catalyst and brought people together," says John. "We knew we had to go out and tear down the roots by hand."

A call for help went out across Scotland to ask for volunteers to go to the islands. Close to 1000 people answered.

"We've had volunteers who've come back repeatedly to offer help," says John. "Some have been out more than 100 times, including one lady who is about 80-years-old."

"That would be Margaret," says Eileen, "she's fantastic".

Jumping aboard the boats as many times a year as they can out-with breeding season, volunteers clamber into vessels to head out to the islands, their bodies swaying in rhythm with the sea swell .

"It's just so fresh when you arrive there," says Eileen. "You smell the salt from the seaweed and you hear the cry from the gulls. They call out at you from the moment you arrive until you leave.

"They're very chatty. It's one of the things that I love about it. Multiply the normal noise you hear from a few gulls on the shore by about 1000 and that's the racket you hear."

Thanks to the dedicated support of the volunteers, the tree mallow continues to be driven back, so much so that today puffin numbers on the islands have risen to over 5000 pairs.

"The puffins are there again and it's wonderful for people to see them," says John. "The volunteers have been wonderful in the support that they've given. It's what has made this particular project worthwhile for me."

While the rising numbers have given hope to the future survival of the birds, conservationists remain "deeply concerned" over the issue of Scotland's declining seabird populations.

In December 2015 puffins were added to the International Union for Conservation of Nature's (IUCU) Red List of Threatened Species for the first time and earlier this year, Tom Brock, chief executive of the Scottish Seabird Centre, told the Herald that "much more work on issues including marine litter was needed".

In the meantime, the volunteers say they pledge to continue to go out as often as they are able each year to beat back the tree mallow for the puffins and openly encourage others to join them.

Walking boots and waterproofs are essential for volunteers as is a decent cup of tea when the cooler sea winds pick up.

"But the highlight is that moment, sometimes, when you sit quietly and hear the puffins calling from the burrows," says Eileen.

"That's when you know you're making a difference."

For more information on SOS Puffin or to view the puffins live on Burrow Cam, you can visit the Scottish Seabird Centre website.