NOT a single Dartford warbler showed its head above the gorse as we strolled across the heath in the sunshine.

But we knew that hidden among the purple heather, a gem among many gems in the Purbecks, were around 60 pairs of the long-tailed bird.

This is a huge success story for Arne, the RSPB's reserve on the edge of Poole Harbour, which is celebrating its 40th birthday.

"When I was growing up 35-40 years ago, the Dartford warbler was the rarest bird in Britain," said South Dorset MP Jim Knight, Minister for Biodiversity.

He said he was delighted it had survived and prospered in this small part of Dorset. "It is still the icon of this place," he added.

Following the harsh winter of 1963, the bird was nearly wiped out.

When the RSPB leased land for this nature reserve in 1965 there were only 11 known pairs in the UK, two of which were clinging on by their claws at Arne.

Hard work in restoring heathland, grubbing up pines and rhododendrons, has seen the range of the singing, wine-red bird expand and its status fall down the endangered traffic-light system from red to amber.

The minister was among guests celebrating the birthday bash of the popular reserve, which attracts 55,000 visitors a year.

Hidden away in a beautiful corner of the harbour, its 1,322 acres include a variety of habitats including woodland, reed beds and salt marsh.

Pausing at a view across Middlebere Channel, warden Neil Gartshore pointed out that neighbouring English nature and Ministry of Defence land gave miles of uninterrupted heathland.

"This allows animals to move between different heaths. A lot of heaths are very fragmented," he said.

Apart from the success story of the Dartford warbler, there are 28 pairs of nocturnal nightjar and two pairs of singing woodlark.

In winter thousands of wading birds, ducks and geese visit the harbour and it is designated an internationally important wetland site for birds because of the numbers it supports.

But there is a lot more to Arne than the wide variety of birds that can be seen there and the deer.

The reserve supports all six species of UK reptiles: adders, grass snakes, smooth snakes, sand lizards, common lizards and slow worms.

And it is one of the top 10 RSPB reserves for dragonflies, with 23 different species buzzing about, 18 of which breed - providing food for the hobby hawk.

"We have worked with partners to create some really significant changes of land in this area," said Tony Richardson, regional director of the RSPB.

"It's not just about a land resource for wildlife. It's an important resource for people.

"The future of this area will only be secured with long term support from government, financial support from visitors and people," he said.

It costs £350,000 a year to maintain the reserve and Arne is one of 16 run by the bird charity in the South West.

The acquisition of more land in 1980, and a farm in 2001, has created a reserve managed by eight staff, helped out by around 100 volunteers.

Now another secretive and red listed bird, the bittern, has been heard booming - its mating call - and another great success story could be building up.