The woodlark, one of England's most critically endangered birds, is making a dramatic comeback, the RSPB has said.
In the last 10 years, numbers have almost doubled from 1,633 breeding pairs in the UK in 1997 to 3,084 pairs, according to the charity's survey.
But conservationists fear woodlarks' good fortune may be short-lived.
They say that undisturbed and untilled farmland where the birds like to nest may begin to disappear as pressure to use land for biofuels increases.
Refuge for wildlife
Sue Armstrong-Brown, the RSPB's head of conservation, said: "The return of the woodlark to our fields, heaths and forests is brilliant news - and shows how important set-aside (land) has become as a refuge for wildlife on our farmland."
But she warned it was crucial their recovery was not "sabotaged" and called for increased efforts to restore and manage lowland heaths to create suitable conditions for the birds.
The woodlark was first red-listed as a species of conservation concern in the 1980s following a dramatic decline in its population in the previous two decades.
At its lowest point in 1986, there were just 241 breeding pairs.
Its decline coincided with the loss of traditional farmland in the south west of England and Wales, and the loss of heathland across the UK.
However, the European agricultural policy of the early 1990s proved an unlikely saviour.
Farmers were paid to take land out of production to reduce EU "food mountains".
It became known as set-aside land and proved a boon to wildlife, including the woodlark.