The red grouse is a bird of heather moorland with a range restricted to areas of blanket bog and upland shrub heath. It is a subspecies of the willow grouse (L. l. lagopus), whose range extends across the northern latitudes of Europe, Asia and North America. The red grouse differs by not developing white plumage during winter and having a diet almost exclusively of heather.
Since the mid-1800s, many areas of heather have been managed to produce grouse for shooting. Indeed, grouse shooting has been one of the major land uses of upland ground and an important source of income for many estates.
We estimate that the numbers of grouse shot per year between 1911 and 1980 has fallen by 82%. Particularly severe long-term declines occurred after the Second World War and after the mid-1970s in Scotland and Wales. In recent history, grouse numbers have remained stable on many English moors, although 2011 and 2012 counts by the Trust recorded record years since our counting began despite the poor weather in 2012. We put these recent successes down to the new form of medicated grit developed by our research. Spring densities in Scotland were similar to 2011 and grouse generally bred well despite the poor weather of 2012 but grouse densities were down 9% on 2011.
The causes of these declines appear to be multifactorial. On a national basis, there was a 30% loss of heather between 1950 and 1980, largely due to over-grazing by sheep and conversion to forestry. Increased winter grazing by sheep, and in some areas by deer, may also be reducing heather quality. However, while heather loss is important, it cannot account for the full extent of the decline in grouse stocks.
There is considerable evidence that the abundance of many grouse predators has increased in recent decades, while the area of land covered by the activities of gamekeepers has declined. In particular, there is evidence of increases in foxes, crows and raptors in many parts of Scotland and Wales. It seems likely that predation pressure, both by mammals and other predatory birds, has increased on many moors. These increases in predator numbers are a significant factor in suppressing grouse numbers, slowing population growth rates and reducing shooting bags on many moors.
Approximately one third of grouse moors carry louping ill, a viral disease transmitted between host animals by ticks. The presence of louping ill causes reduced levels of chick survival, with up to 80% of infected chicks dying. As a consequence, chick survival rates average 50% lower on moors with louping ill.
The nematode worm Trichostrongylus tenuis, the causative agent of the disease strongylosis, is widespread in red grouse and high levels of infection can cause significant reductions in both breeding success and direct mortality. Research in the north of England has shown that this parasite is largely responsible for the cyclical fluctuations in grouse numbers on moors in this region. The parasite is most prevalent when grouse stocks have been high in the previous year, but it may also reduce breeding success on low-density moors.
The Trust can provide you with advice about managing grouse populations and moorland through Grouse Technical Services.