Causes of change

Longer-term trends in Red Grouse abundance are overlain by cycles, with periods that vary regionally, linked to the dynamics of infection by a nematode parasite and to interrelated variations in the aggressiveness of males in autumn.

Further information on causes of change

Given its economic significance, long-term population trends of Red Grouse are likely to be closely associated with changes in management practices (see below). Shooting bags have revealed long-term declines, apparently driven by a combination of a loss of heather moorland, increased predation from corvids and foxes, and an increasing incidence of viral disease (Hudson 1992, Newton 2004). However, these trends appear to be overlain by cycles, with periods that vary regionally, linked to the dynamics of infection by a nematode parasite Trichostrongylus tenuis (Dobson & Hudson 1992, Gibbons et al. 1993) and to interrelated variations in the aggressiveness of males in autumn (Martinez-Padilla et al. 2014). Recent increases in the Red Grouse population have been attributed to the use of higher strengths of medicated grit (Thompson et al. 2016).

Strip burning of heather is undertaken to increase suitable habitat for Red Grouse. Although the short-term effect is to reduce the abundance of birds using the recently burnt areas (Douglas et al. 2017), densities subsequently increase most in areas where heather recovery is greatest (Ludwig et al. 2018c). Analysis of game bag data since 1890 linked population changes to changes in keeper density and afforestation (Robertson et al. 2017). However the wider environmental impacts of moorland management for grouse are contested (Thompson et al. 2016, Sotherton et al. 2017). Whilst long-term declines are most likely linked to habitat changes (Thirgood et al. 2000), raptor predation may subsequently have limited population growth at some sites (Thirgood et al. 2000, Roos et al. 2018). In a study looking at four upland areas in the UK, higher Red Grouse abundance was correlated positively with higher predator control (Buchanan et al. 2017), and abundance and breeding success was higher at a Scottish site in years when predators were controlled (Ludwig et al. 2017). Other studies have concluded that mortality associated with raptors are important factors in survival but could not exclude scavenging so may have over-estimated true predation (Ludwig et al. 2018b, Francksen et al. 2019).

Hen Harriers in particular can reduce grouse shooting bags, limit grouse populations and cause economic losses to moor owners, which has led to instances of illegal persecution (Thompson et al. 2009, 2016, Murgatroyd et al. 2019; see also Conservation Actions section, below).

Laying dates in the Scottish Highlands advanced by about ten days between 1992 and 2011, and were inversely correlated with pre-laying temperatures, but no overall effect of climate change on chick survival could be identified (Fletcher et al. 2013).

At Langholm Moor, Red Grouse productivity was lower, suggesting higher chick predation, in years with high vole abundance; the reasons for this were unclear but were believed to be more consistent with the hypothesis that 'apparent competition' was occurring between voles and grouse, rather than the 'alternative prey' hypothesis, i.e. that incidental grouse chick predation is higher when increased vole numbers attract more predators (Ludwig et al. 2020b).

Information about conservation actions

This species is Amber-listed in the UK due to its European status; however, the fluctuating BBS trend does not raise any alerts and so does not give cause for concern. The species benefits from intensive management of moorland, to increase numbers available to be shot, and therefore no specific additional conservation actions are currently required.

Some observers have questioned the legitimacy of grouse shooting if it is only viable when birds of prey are routinely killed (Thompson et al. 2009), whilst others contend that grouse shooting protects the conservation of heather moorland and hence populations of some declining birds such as waders that depend upon it (Sotherton et al. 2009). The relative importance of predation and habitat management on numbers of Red Grouse, and on the wider environment including other moorland birds, in particular Hen Harrier, is the source of much debate with strongly opposing views (Redpath & Thirgood 2008, Thompson et al. 2016, Sotherton et al. 2017, Hodgson et al. 2018, 2019, St John et al. 2018). This has consequences for wider moorland management and the bird populations that live there (Redpath & Thirgood 2009, Thompson et al. 2016). The final report of the Langholm Moor Demonstration project concluded that whilst some targets had been met, the project was unable to achieve compatibility for management between raptor and Red Grouse interests and grouse numbers remained insufficient to make driven shooting viable (LMDP Partners 2019).