The black grouse is a potent symbol of the way in which land-use changes in the uplands have affected biodiversity.
Agricultural practices during the last forty years have substantially changed the landscape mosaic which black grouse require. Encouraged by production subsidies, rough grazing land has been drained, ploughed and re-seeded, encouraging the growth of rye grass at the expense of heather and other dwarf shrubs, so that more sheep can graze. These fields are regularly fertilised, reducing the variety of grass species.
Heavy grazing by sheep, deer and rabbits reduces the amount of tall vegetation which the grouse require for shelter, perhaps making them more vulnerable to predation, and can lead to conversion of dwarf shrub dominated vegetation to grasses, hence reducing the food availability. Drainage removes wet flushes containing invertebrates which are so vital to black grouse chicks in their first few weeks of life.
As commercial forestry plantations have matured, the dwarf shrubs (such as heather, which adult grouse require for food and shelter) are lost, since they cannot tolerate the deep shade under the trees. For instance, in the Åland archipelago in the Baltic, the 80 per cent reduction in black grouse populations since 1940 was directly attributable to the afforestation of grouse habitat.
It may also have been a major factor in the decline of black grouse in Wales in the 1980s, though this occurred at the same time as increased levels of grazing. Deer fences erected to protect forestry plantations can be a significant cause of adult mortality.
Populations fluctuate because of the weather. A cold, wet June can limit the abundance of insects and increase the chances of young birds becoming chilled. Predation by foxes and crows can become particularly important when hungry, noisy chicks are looking for food.