By Alex Kirby BBC News Online environment correspondent

The number of starlings seen in UK gardens has fallen by two-thirds since 1979.

House sparrow sightings have also declined, though less steeply.

But some other species, including tropical birds that have escaped from captivity, are spreading further afield.

The findings, published by the Royal Society for the Protection of Birds (RSPB), are the result of observations by more than a quarter of a million people.

All took part in the RSPB's 2002 Big Garden Birdwatch, held during the last weekend in January.

Winners and losers

The RSPB asked participants to spend an hour counting the birds in their garden, school grounds or local park, and to record the highest number of each species seen at any one time.

It had hoped to double the 52,000 involved in 2001. In the event, 262,000 people took part.

Starlings are much scarcer than they were

Starlings were the commonest birds seen, followed by house sparrows, blue tits, blackbirds, chaffinches, greenfinches, collared doves, great tits, wood pigeons and robins.

But behind the bare figures lies a more intriguing story - why some birds are doing well and others are not.

In 1979, the average number of starlings seen in each garden was 15. This year it was 4.2. House sparrows, the second commonest birds, fell from 10 in 1979 to 4 this year.

Andrew South of the RSPB told BBC News Online: "There is something not quite right about the starling and house sparrow figures, and it seems to be happening fairly suddenly.

"We began to get reports in the mid-1990s that people were seeing fewer of both species, and we didn't take too much notice to start with.

Shy magpies

"But now these Birdwatch figures are showing that they were right all along.

"We're very concerned about farmland birds, and garden sightings for one of those - the songthrush - have declined from an average of 0.6 in 1979 to 0.2 this year."

Parakeet: A migrant who's settled in

But blue tits, third on the list, are showing an increase, up from an average of 2.4 per garden in 1979 to 3.2 today, suggesting their woodland habitats are improving.

Another surprise from the survey is the absence of the ubiquitous magpie from the top 10.

The collared dove, in at number seven, is not a UK native, but has established itself well enough to spread. And before long the list may include another immigrant, the ring-necked parakeet.

Andrew South said: "The parakeets look likely to be the collared doves of the new century.

"They've settled in the wild in their thousands, although they're a tropical species brought here as caged birds.

"It's only about five years ago that they were recognised as British birds at all."