The number of birds visiting British gardens is on the decline, according to a survey involving 470,000 people.

Although the house sparrow continued to be the most common garden bird, its numbers have dropped from an average of 10 per garden in 1979 to 4.4 in 2006.

The starling, once the most common, is down to a quarter of those in 1979.

Some 86,000 children were among those who watched gardens and parks in the Royal Society for the Protection of Birds's January Big Garden Birdwatch.

The numbers involved broke the previous record set in 2004 of 419,000 participants.

The house sparrow was the most common bird seen over the two days - although the blackbird, recorded in 94% of all 270,000 gardens involved, was the most widespread - and 8.1m birds of 80 species were seen.

TOP 10 2006 SPECIESBlue tits. Image: Mike Read/rspb-images.comBlackbird - 94.71%Blue tit - 84.44%Robin - 84.19%House sparrow - 67.71%Chaffinch - 58.99%Collared dove - 58.54%Woodpigeon - 57.28%Great tit - 57.10%Starling - 50.95%Greenfinch - 45.25%(Numbers are the percentage of gardens the species were seen in)

Co-ordinator Richard Bashford told BBC Radio 4's Today programme "a lack of food for the chicks" was causing the fall in the number of house sparrow sightings.

Bird-lovers should leave food out and allow their garden grass to grow to create a better environment for birds to catch insects, he added.

However, some bird species have increased, with the greenfinch population growing 67% in the past 27 years and the wren jumping 140%.

Many people spotted more blackbirds and song thrushes, and other less common species.

There had been an "amazing rise in small finches", Mr Bashford told Today.

"The number of siskins, which are super colourful birds, was up by 483% from last year, and bramblings were up by 371%.

"This highlights the importance of our gardens to birds coming to the UK in search of food and shelter and escaping the harsh winter weather on the continent."

The survey had been "extremely well supported... even in the most built-up areas where you might not expect people to watch birds," Mr Bashford added.

"In Greater London, nearly 30,000 people spotted 400,000 birds this year.

"It is fantastic there is so much interest in the wildlife around us with more people then ever enjoying the birds in their gardens."