Red kites, the majestic birds of prey which 20 years ago were one of Britain's rarest creatures and confined to the Welsh mountains, are now being regularly seen in gardens around Britain, the Royal Society for the Protection of Birds has found.

A record number were spotted during this year's RSPB Big Garden Birdwatch, the latest signal that the bird's reintroduction programme has been an enormous success.

There was an increase of more than 130 per cent since last year in kite sightings during the weekend of the survey, and they moved to number 53 in the rankings of most frequently seen birds in gardens, ahead of more familiar species such as tawny owls and chiffchaffs.

Once common all over Britain, even in the streets of London – Shakespeare refers to them frequently – red kites were gradually driven to extinction by persecution everywhere except central Wales, where a small population stubbornly clung on in the Cambrian mountains.

But a series of red kite reintroductions across the UK, which began in 1990, have proved to be one of the greatest conservation success stories ever. In some parts of Britain, such as the Chilterns, red kites are now common and 7 per cent of the world's red kite population is now in the UK.

This year, more than 600,000 people took part in Birdwatch, thought to be the biggest "citizen science" exercise in the world. Only the birds that landed in gardens were officially recorded, but numerous comments on survey forms and online forums suggest even more red kites were seen flying over gardens, and the results are further proof that the birds are continuing to flourish.

"We were delighted to see red kites appearing on so many survey results forms," said Sarah Kelly, the Big Garden Birdwatch co-ordinator.

Jeff Knott, RSPB species policy officer, said: "Red kites are one of our most elegant birds of prey and they are a spectacular sight. I defy anyone that gets to see them flying over their garden not to be in awe of them, and the increase in Big Garden Birdwatch sightings is great news for both the public and the birds themselves."

While red kites are doing very well in the UK, elsewhere in Europe they continue to be badly affected by illegal poisoning. With big declines in the species' core range, the importance of the UK for red kites in global terms seems likely to increase further over the coming years.