Fears have been raised that half to three-quarters of the rare Dartford warbler in Hampshire may have perished during the icy weather.

In neighbouring Dorset, disaster is thought to have been averted, with the majority of rare heathland birds surviving the Arctic blast.

But prolonged cold snaps can be the death knell for the striking bird with its ruddy breast and long tail, which sings in spring from the top of gorse bushes.

The prolonged snowfalls in 1962/3 decimated the warbler, which in England is at the northern edge of its range, leaving only 11 pairs identified across the entire country.

It recovered from the edge of extinction and a national survey in 2006 estimated 3,212 pairs across the UK, a 70 per cent increase from the previous survey in 1994.

Poole has many pockets of urban heath where the birds feed on insects and berries found in gorse and heather.

Jez Martin, nature conservation officer at the Borough of Poole, said: “It will have done for one or two but I can’t see it being significant.

“The winter of 1995, when there was lots of frost, took out a third of the population of Canford Heath. It went from 38 pairs to 25 pairs. That’s one per cent of the national population.”

However the greatest danger to the birds’ perilous existence came not from the cold but from the heat. Devastating heath fires destroy the birds’ habitat which takes years to recover.

“We had lots of fires in 1995 and it really wasn’t until 2005 that we got back to the same number of pairs we had 10-years previously,” he said.