As a species hen harriers are not endangered, as they have a circumpolar breeding distribution throughout northern Europe, Asia and North America (where it is known as the northern harrier, and may be a distinct species, though closely related).
It is one of the most successful and widespread of raptors.
Hen harriers do, however, face extinction in England, where only one pair nested successfully last year.
Thus the RSPB is being a little misleading, but not inaccurate, with its use of the word extinction.
Several hundred pairs breed in Scotland, where numbers are relatively stable, while on Orkney numbers are actually increasing.