Since 1998, numbers of the songbird have dropped by 50 per cent Scientists now want to establish where in Africa it spends its winter - a location which remains a mystery The nightingale could become extinct in Britain within 30 years if nothing is done to stop its rapid decline, scientists have warned. Researchers want to establish where in Africa the songbird spends its winter - a location which remains a mystery - before it disappears altogether. Since 1998, numbers of the iconic bird have dropped by 50 per cent as its former breeding grounds empty. An increase in grazing deer in the UK has contributed, said the British Trust for Ornithology (BTO), with the sub-soil favoured by the secretive birds being destroyed. But the decline may also be taking place along its lengthy migration route, which sees it spend the winters in sub-Saharan Africa. Paul Stancliff, a spokesman for BTO, said more research was needed to establish precisely where the birds winter, and if there were environmental changes en route which were also contributing to the fall. Despite attempts, only one bird has ever been tracked to its winter stopover. He said: 'If the rate of decline continues the breeding population in the UK will be at very low levels in ten years time and in 20 or 30 years it drops off the graph - it becomes extinct as a breeding bird. 'It's an iconic species and that's a scary thought.' He said that in Britain, nightingales living in woodland had been more affected than those living in scrub or fenland - their other habitat. He said: 'In one area, Bradfield Woods in Suffolk, seven years ago there were 12 pairs of nightingales. Three years ago this was down to one and last year there were none. 'There have been changes of management to woodlands, with more coppicing, which is affecting the undersoil that they like. They are very secretive birds. 'There has also been a large increase in a number of species of deer, particularly the Muntjac. They browse the undersoil and clear out the woodlands and make it unsuitable for nightingales.' But this would not fully explain the decline, he said, and more information was needed on their migration. Previous research has seen tracking devices fitted to the birds, but only one came back with a successful reading - showing it had wintered in Guinea-Bissau. But Mr Stancliff said: 'We don't really have any idea where they spend their winter and we have to look into that further. 'The human population is growing in that part of West Africa, and, for example, goats could be creating the undersoil lack that we have here.' The nightingale which was successfully tracked had flown through Europe before spending three weeks in Portugal, before heading across the Atlantic, through Senegal and to Guinea-Bissau. Changes in environment anywhere along the route - for example a decline in the cork oak industry in Portugal - could all be having an effect. The BTO has launched the Nightingale Appeal and an accompanying CD of Nightingale song with the profits funding research into the bird.