The RSPB is calling on the government not to abandon its rare bird registration system which it says is essential in preventing wildlife crime.
The peregrine falcon became a UK protected species in the 1960s
The society is concerned cost-cutting could signal the end of the scheme under which anyone keeping captive-bred wild birds must have them registered.
Scrapping the system would lead to a sharp rise in thefts of wild birds from nests, it warns.
Ministers are expected to make a decision on the scheme soon.
Currently, anyone keeping any of Britain's rarest birds, such as golden eagles or peregrine falcons, has to register the birds under the Wildlife and Countryside Act.
The RSPB says such registration has proved to be "one of the most effective weapons in fighting wildlife crime".
The society says that once the authorities know where birds are, they are able to build up family histories of legally captive-bred birds.
Then through DNA, they can prove when suspect juvenile birds have been illegally taken from the wild and "laundered" into the lucrative market for captive-bred birds.
RSPB figures show that prosecutions involving two of the most valuable species, the peregrine falcon and the goshawk, have fallen dramatically since DNA evidence was first used in criminal prosecutions in the mid-1990s.
Duncan McNiven, from the RSPB, told BBC Five Live that ministers should consider the issue of registration carefully.
"We can only use DNA testing if we know where the birds are and who the birds are all related to.
"That's the beauty of registration - it requires the keepers of the birds to tell the government where the birds are, what their identity is and who they're related to so you get family trees built up.
"And it can be proved one way or the other whether they're taken from the wild illegally, or whether they're legally captive bred."
The RSPB's call has been backed by the police.
Richard Brunstrom, chief constable for North Wales and the lead officer on wildlife crime for the Association of Chief Police Officers, described the measures as "conservation legislation with a clear purpose".
"It should not be weakened or dismissed in some dogmatic government anti-bureaucracy drive without real thought being given to the consequences, which could be catastrophic for species' conservation."
Biodiversity minister Joan Ruddock is expected to make a decision on the future of the registration system shortly.