Blakeney Point, a remote outcrop linked to the Norfolk coast by a narrow three-mile shingle promontory, has only three human inhabitants but they are not alone. They share the pebble beaches with about 5,000 seabirds, which live in tightly packed colonies stretching from the sand dunes to the tideline.

This outcrop is where, 100 years ago this month, the first birds were tagged with numbered metal leg bands in the British bird-ringing scheme, which is still running today. The job of Blakeney’s three coastal wardens, who spend their time monitoring the colony’s blackheaded gulls and four varieties of tern, has changed little since 1909.

Although a record number of birds are being tagged today, the wardens face a serious problem: people are no longer returning the rings, making it increasingly difficult to track where birds go and how long they survive.

The practice is dependent on the public posting rings found on dead birds, providing the date and location where the bird was found. Since the 1950s, when the ringing scheme had a return rate of around 4 per cent, the number of rings coming back has plummeted. In 2006, the most recent year on record, about 1 per cent of rings were returned.

The drastic fall has been put down to people not spending as much time in the countryside or on remote beaches, an increasing reluctance to post letters, and simply being more squeamish than they were 50 years ago. “People are terrified of touching something that’s dead. And now bird flu has made it even worse,” said Mark Grantham, a research ecologist at the British Trust for Ornithology (BTO).

Edward Stubbings, one of the coastal wardens, said that Blakeney’s black-headed gulls and four varieties of tern — the common tern, sandwich tern, little tern and Arctic tern — are thriving.

The sky over the end of the point is filled with the elegant black and white fork-tailed birds, which let out harsh calls between swooping to pick out sand eel fry from the sea. The beaches, cordoned off from the public, are scattered with nests — roughly carved out hollows in the sand, lined with seashells, and brimming with eggs and fledgeling birds.

A year ago the picture was different. “The colonies were completely deserted,” Mr Grantham said. “Some years they turn up, there’s not enough food, and they just leave again without breeding.”

The tagging scheme is the only reliable way of charting changes in population, and linking them to environmental factors, such as variations in winter temperatures, and the position of the Gulf Stream.

Fewer rings being returned means scientists have less data from which to infer survival rates, and so estimates are less precise. In turn, this makes it difficult to identify and promote appropriate conservation measures.

“It’s a huge problem,” Mr Grantham said. “It means there’s a lot more uncertainty about our figures, which makes it harder to sell our recommendations to politicians and decision-makers.”

About 800,000 birds are ringed each year in Britain, mostly by the BTO, the Royal Society for the Protection of Birds and private individuals. The technique remains the primary way to observe where birds go and how long they live, and is crucial for scientists monitoring how bird populations are coping with changes in climate and agricultural practice.

Because the data is less precise, it can take ornithologists longer to detect sudden declines in populations. In the most recent survey, published in May, one in five breeds of British bird was “red listed” — having suffered a population decline of more than 50 per cent in the past 25 years.

In an attempt to counter low returns, British bird-ringers have set up a website where people can provide ring details without having to post the ring itself. The BTO says this is already helping increase the return rate.

In the US a study suggested financial incentives helped to increase return rates. When a reward of $75 (£45) was promised, the return rate rose dramatically. However, this was not only expensive, but birds were shot for the rings.

Ringing the changes

• In 1899 Christian Mortensen, a Danish school teacher, started the first bird-ringing scheme.

• In 1909 two projects were started by Arthur Landsborough Thomson in Aberdeen and Harry Witherby in England.

• In 1911 a birdwatcher was met with scepticism when he wrote to Country Life magazine claiming that he had received a swallow ring from South Africa. We now know that British birds have flown as far as Australia.

• In the 1950s mist nets — fine meshes with pockets that catch birds in flight — were invented.

• Since 1909 more than 36 million birds have been ringed in Britain.

• The European Union has launched a co-ordinated bird-ringing website at www.ring.ac.

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