GROWING numbers of migratory birds are too lazy to fly all the way to Africa for the winter and are staying in Britain.

Unprecedented numbers of warblers, blackcaps and chiffchaffs shirked the flight to warmer climes last year and even more are expected to stay this winter. Most surprising is the number of species of warblers that can now be found in Britain in the coldest months, according to a survey by the British Trust for Ornithology (BTO).

Greg Conway, who organised the survey for the trust, said: “It’s as if they’re saying, ‘I can’t be bothered to go abroad this year, dear — let’s stay here’. They’re too lazy to migrate to Africa.”

Many species of warbler were seen in Britain between November last year and March this year when they should have been in West Africa. The numbers of these birds are small and most are likely to die because the climate is still, despite global warming, too cold for them.

They are, however, following the same pattern of migratory route change that has preceded a big increase in the numbers of blackcaps and chiffchaffs. In the 1960s it was rarer to see a blackcap than it is to see one of the migratory warblers today but in the 1970s a few began to stay and now there are estimated to be thousands.

According to Graham Appleton, of the BTO, the “exponential” increase in blackcap numbers in the past 30 years has demonstrated “evolution in action”.

Blackcaps do breed in Britain in the summer but the birds staying during the winter have migrated from Germany. These German blackcaps should be in North and West Africa but have discovered that by flying instead to Britain they are in pole position to get the best breeding territories in Germany in the spring. They now breed more successfully than the blackcaps that migrate to Africa.

Mr Appleton said that with average temperatures predicted to rise steadily over the next century it is possible that in 10 or 20 years the migrating warblers will become established as birds wintering in Britain.

The survey is to be repeated this winter and the BTO hopes that more volunteers will come forward to report on the birds that they have seen. Last winter there were more than 1,000 observers.

At the same time as announcing the benefits of global warming for migratory species the BTO revealed that four types of bird had been added to its “of concern” list for breeding levels. The skylark, spotted flycatcher, starling and mistle thrush were added to the nest record scheme’s concern list because brood numbers have slumped. Two species, the lapwing and the bullfinch, were removed from the list.

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