Yes, that really is a vulture in the garden

Exotic birds are now permanently resident in the UK - and your help is needed to survey their populations

"Oh, look, darling, there's an eagle owl on our lawn. And an orange parrot on the bird table. And what's that perched on the fence? Why, it's a vulture! Quick, where are my binoculars?"

The scene is a home overlooking an ordinary English garden. Inside are two of the hundreds of thousands of Britons who monitor their local wildlife; outside, attracted by the seeds and bacon rind kindly provided, are some of the exotic species now appearing in our gardens. Birdwatching is changing, and on the eve of the biggest ever survey of garden birds, the scale of rare, colourful and plain alien species in the UK has been revealed.

In recent years, the British Trust for Ornithology (BTO) has spotted eagle owls in Derbyshire, a Lady Amherst's pheasant in Suffolk, a burrowing parrot in Chepstow, Himalayan pheasants, black swans, tropical sunbirds, ring-necked parakeets and a further 20 species of parrot. Leicester gardens have produced a crested mynah and a turquoisine parakeet, while orange-winged parakeets have popped up in Weybridge, Surrey, and South American monk parakeets have been spotted in Borehamwood, Hertfordshire. Meanwhile, a rose-coloured starling has been sighted in Wales and a turkey vulture has shown up in Cambridgeshire.

Some, like the eagle owl, in Yorkshire, and ring-necked parakeets (almost a menace in parts of London) are now established, but most of the others are escapees from captivity or bewildered cast-offs of the exotic bird trade.

On 28 and 29 January there will be an opportunity to add to that list, when the Royal Society for the Protection of Birds holds its 28th annual Big Garden Birdwatch, urging the nation to do an hour of backyard twitching. Last year, 400,000 people took part.

Additional reporting by Sion Morgan

To participate in the Big Garden Birdwatch, go to www.rspb.org.uk or ring 0870 6007108. To join the BTO's project, go to www.bto.org/gbw, or ring 01842 750050