The decline of the nightingale in the UK could be due to changes in its habitat along its migratory route to Africa, a study has shown.
Last year Anglian Water and the British Trust for Ornithology (BTO) fitted 10 birds at Grafham Water in Cambridgeshire with tracking devices.
Seven birds have come back with data about their 3,000 mile (4,828 km) journey to Senegal and The Gambia.
The tracker information will be fully analysed by the autumn.
A BTO spokesman said nightingale numbers had dropped by more than half since 1995, with only 6,000 singing male nightingales remaining in the UK.
Initial findings from the geolocators show the birds, which weigh about the same as a £2 coin, make the six-week journey to Africa via northern France and Spain to Gibraltar.
They then fly along the African coast to avoid the long flight across the wide, dry Sahara Desert.