A rare bird which sounds like a motorbike is making a comeback.

The number of nightjars in Sussex has increased by 68 per cent since 1992.

The dove-sized bird is usually heard at dusk and is difficult to spot because it looks like bracken.

It comes to Britain in the summer from Africa and is one of the 40 most threatened birds in the UK.

Sussex has an estimated 243 males, representing six per cent of the national total.

The birds were counted by volunteers undertaking a national survey commissioned by the RSPB, British Trust for Ornithology, English Nature and Forestry Commission England.

Up to 1,000 people visited heathland and forestry plantations at dusk and dawn to listen for the distinctive sound made by male nightjars, which sounds like a distant motorbike and can last up to nine minutes.

The survey revealed there are more than 4,000 male nightjars in the UK.

Paul Spiers, assistant warden of the RSPB's Pulborough Brooks reserve, where 28 hectares of heathland is being restored to attract nightjars and other rare species, said: "Up to the Fifties, the nightjar was more widespread but the population declined considerably by the early Eighties.

"It is great to see the nightjar responding so well."