New research by the RSPB has shown that decreased grazing and appropriate habitat are essential for hen harrier survival. This is despite the RSPB previously attributing the birds? decline in England largely to persecution by
gamekeepers. Scientists found that hen harrier productivity is directly related to the stocking densities of sheep in its main breeding and hunting areas. Over the period that sheep numbers declined, the study revealed a significant increase in both rough grassland and voles, which are a prey species for harriers.