Researchers want to establish where in Africa the birds spend their winter - a location which remains a mystery - before they disappear altogether.
Since 1998, numbers of the iconic songbird have dropped by 50 per cent as its former breeding grounds empty.
An increase in deer in the UK has contributed, says the British Trust for Ornithology, with the sub soil favoured by the secretive birds being destroyed.
The decline may also be taking place along its lengthy migration route, which sees it spend the winters in Sub-Saharan Africa.
Paul Stancliff, of the BTO, 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."