The Dartford warbler (Sylvia undata) unlike most other members of its family, is a year-round UK resident, but suffers in cold weather. Severe winters in the early 1960s cut the national breeding population to just 11 pairs.
However, there are now believed to be about 2,000 pairs, and they may soon recolonise areas not occupied since the 1930s. "It's turning into a most heartening success story," said Robin Hynde, policy officer for the Royal Society for the Protection of Birds. "The population is probably higher now than for a very long time, owing to a combination of good habitat management on a number of nature reserves and the fact we haven't had any really severe winters since the early 1980s.
"Future severe winters may result in reductions, but one hope is that habitat management will boost their survival chances and provide potential for fast recoveries."
In 1974, the number of pairs had increased to 565 but after severe winters in the late 1970s and early 1980s the total had fallen to 423 by 1984. However, when the survey was repeated in 1994, the population had risen to more than 1,600.
Dartford warblers are dark grey, with pinkish-brown underparts, and distinctive, often cocked tails, which account for half their five-inch length.
Most are found in Mediterranean regions, with up to one million pairs in France. In England, their most northerly outpost, they skulk among gorse clumps.
"We have seen a consolidation in their core areas - Dorset, Hampshire, Sussex and Surrey - and signs of northward expansion into Berkshire, where the species ceased nesting in the 1940s, and Suffolk where they disappeared in the 1930s," said Mr Hynde.
Earlier this year there was even a sighting on a heathland nature reserve at Heswall on the Wirral.
There are hopes that the population will return to 19th- century levels, when birds nested from Cornwall to Kent, with isolated colonies as far north as Shropshire and Staffordshire.
The species was first identified in Kent in 1787. A scheme to recreate heathland at Tudeley Woods, near Tonbridge, could eventually bring it back to within 20 miles of the place after which it was named.
Mr Hynde said the warblers were benefiting from heathland conservation on RSPB reserves at Arne, Dorset, and Aylesbeare Common, Devon, and at sanctuaries under the care of various wildlife trusts and English Nature.
"This is a habitat important to other birds, such as nightjars and woodlarks, as well as reptiles like smooth snake and sand lizard and a range of plants, so there are widespread benefits."
The Government has set a target to re-establish 14,000 acres of heathland.Reuse content