The fate of the red-backed shrike and the wryneck, which were found throughout the country a century ago, is puzzling experts.

Numbers have declined since the 1950s but nevertheless these migrant birds continued to breed in Britain until 1998 and many from Scandinavia had also appeared to colonise parts of Scotland. But birdwatchers who collate sightings have reported “nil returns”.

Graham Madge, spokesman for the Royal Society for the Protection of Birds, said: “We can’t say yet they are extinct because they are migrant birds and could turn up at any time but we are saying they are virtually extinct.”

One of the theories for their disappearance is a decline in numbers on the continent where farmers use powerful pesticides which kill large insects that the birds feed on.

Another possible reason is that collectors of birds’ eggs, aware that the species is becoming rarer, may have stolen eggs.

Mr Madge said: “The eggs of these birds are now highly prized because these birds are such a rarity and it is likely that these collectors have pushed the birds over the edge.” He hoped though that with climate change the birds may recover as they thrive in warm temperatures and benefit from warmer summers.

The red-backed shrike is identified by its red back, black mask and white underbelly, and the wryneck, the smallest European woodpecker, is noted for the mottled marks on its grey and brown plumage.

Other birds which continue to decline in numbers are the willow tit, down 72 per cent in eight years, the turtle dove, down 42 per cent, and the starling and yellowhammer, both down 13 per cent.

Dedicated conservation efforts at various reserves are also paying off and an attempt to establish the corncrake by the RSPB, English Nature and the Zoological Society of London has met its first success.

A family party of month-old chicks has been sighted on the RSPB’s Nene Washes reserve, near Peterborough.Numbers are also up for other “red list” species of endangered birds such as the stone curlew and cirl bunting, both up 54 per cent, and there are now 55 breeding male bitterns and 2,000 capercaillie thanks to special conservation efforts.

Experts also think that the various countryside stewardship schemes and greener farming practices are beginning to pay dividends with increased numbers too of the tree sparrow, up 54 per cent, and the songthrush, up 13 per cent.

Reintroduction schemes for species such as the osprey, red kite and white-tailed eagle are also yielding encouraging results.

The State of UK Birds 2003 is a report collated by the RSPB, the British Trust for Ornithology and the Wildfowl and Wetlands Trust.

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