The beauty spot is part of the Berwyn Mountains site of special scientific interest, whose protected moors provide ideal habitat for rare birds such as the henharrier and the black grouse.
The status of the henharrier in England is now markedly worse than it was five years ago and it may cease to be a breeding species if the current level of persecution continues, the group says.
The Ouse Washes includes a large floodplain which is looked after by the Royal Society for the Protection of Birds and provides a habitat for the Bewick's swan and whooper swan and wintering birds of prey, including the henharrier, merlin, peregrine falcon and short-eared owl.