The newest members of the EU must learn from the UK's mistake of endangering farmland birds with intensive farming methods, the RSPB warns.
The UK has less than 1% of the EU's population of corncrakes
A BirdLife International report shows that nine of the countries that joined in 2004 have an abundance of farmland birds under threat elsewhere in Europe.
That is because of their large areas of low-intensity farmland, the RSPB says.
It is urging the nine - largely from central and eastern Europe - to use EU payments to maintain numbers.
Special payments are available to help governments preserve countryside as well as wildlife-friendly farming methods.
Payments in the UK and elsewhere in the EU are also available to farmers trying to restore populations of wildlife under threat or close to extinction because of modern methods.
Wildlife-friendly payments are available to UK farmers for measures including:
Mowing meadows late allowing ground nesting birds to flourish
Restoration of landscape elements such as hedgerows
Targeting endangered species with the necessary mix of crops
The report shows that nine of the member states that joined in 2004 - Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia - are home to 98% of the EU's imperial eagles, 92% of its corncrakes, 73% of its white storks and 55% of its roller population.
Poland, which accounts for 10% of all the EU's agricultural land, has more than a quarter of the union's corncrakes.
By comparison, the UK has less than 1% of the EU's population of corncrakes.
The RSPB's Mark Avery said: "Those countries which have most recently joined the EU have brought with them a wealth of wildlife including healthy populations of species which have declined markedly elsewhere in Europe, including the UK.
"Some of these species, like the corncrake, are only just beginning to recover in Britain, thanks to government-funded wildlife-friendly farming schemes and the care invested in their future by groups like the RSPB."
Now that the EU's Common Agricultural Policy governed farming in the nine countries, their "wealth of wildlife" was "increasingly threatened by agricultural intensification and land abandonment", he added.
"We would urge them to use European funds to keep their natural treasures while they still can," he said.
"This approach will also help ensure the economic and social wellbeing of farmers too."