Action: Control predators not on islands for gamebirds
- Four controlled studies in Europe found increased populations or productivity of grouse and partridges on sites with predator removal. One study tested multiple interventions simultaneously.
- A fifth replicated UK study found no increase in grouse densities or reproductive success on sites with gamekeepers, compared to those without.
Supporting evidence from individual studies
A replicated, controlled study in the spring of 1974 on a cereal farm in Villers-Cotterêts, France (Westerskov 1997), found that grey partridges Perdix perdix were significantly more abundant in areas provided with ‘partridge cafeterias’ than in control areas. These ‘cafeterias’ included stoat Mustela ermine box-traps. This study is discussed in ‘Provide supplementary food to increase adult survival’.
A replicated study (Baines 1996) at five sites in northern England and Scotland, found that densities and breeding success of black grouse Tetrao tetrix was no higher on moors with a gamekeeper (and associated predator control) than on moors without a game keeper (average of 1.6 males/km2, 2.3 females/km2 and 1.8 chicks/female on 11 keepered moors vs. 1.9 males/km2, 2.7 females/km2 and 1.9 chicks/female on nine unkeepered moors, n = 9). Moors were an average of 50 km2.
A replicated, controlled study at two farmland and woodland sites in southern England between 1985 and 1990 (Tapper et al. 1996) found that grey partridge Perdix perdix breeding success and brood sizes were significantly higher when predators were controlled, compared to years without removal. This led to August partridge numbers being 75% higher and breeding numbers the next year being 36% higher. Over three years this led to breeding densities that were 2.6 times greater when predators were removed. Predators removed through trapping and shooting were predominantly red foxes Vulpes vulpes, carrion crows Corvus corone and black-billed magpies Pica pica.
A controlled before-and-after study years in northern Scotland between 1989 and 1999 (Summers et al. 2004) found that the breeding productivity of western capercaillie Tetrao urogallus and ‘survival’ rates of 48 artificial nests were higher during the last three years (1994-6) of predator removal, compared to nine sites without predator removal. However, in the previous two years of predator removal (1992-3) and years without removal (1989-91, 1997-9), productivity was lower on the experimental site. In non-removal years, productivity averaged 0.1 chicks/female, compared with 1.4 chicks/female in removal years. Predator removal involved trapping carrion crows Corvus corone (a total of 368) and shooting red foxes Vulpes vulpes (a total of 22 adults and 52 cubs).
A controlled study in 2002-9 on mixed farmland in Hertfordshire, England (Aebischer & Ewald 2010), found that the number of grey partridges Perdix perdix increased significantly on an experimental site, where predators were controlled (along with several other interventions), but only slightly on a control site without predator control. This increase was apparent in spring (from fewer than 3 pairs/km2 in 2002 to 12 pairs/km2 in 2009, with a high of 18 pairs/km2 vs. approximately 1 pair/km2 on the control site in 2002, increasing to approximately 4 pairs/km2 in 2009) and autumn (from fewer than 10 birds/km2 in 2002 to approximately 65 birds/km2 in 2009, with a high of 85 birds/km2 vs. approximately 4 birds/km2 on the control site in 2002, increasing to approximately 15 birds/km2 in 2009). Predators controlled were red fox Vulpes vulpes, stoats Mustela erminea, brown rats Rattus norvegicus, carrion crows Corvus corone and black-billed magpies Pica pica. The experimental site also had supplementary food provided and habitat creation (see ‘Provide supplementary food to increase adult survival’ and ‘Plant wild bird seed or cover mixture’). The effects of agri-environment schemes and the provision of set-aside are also discussed in ‘Pay farmers to cover the costs of conservation measures’ and ‘Provide or retain set-aside’.
- Westerskov K.E. (1977) Covey-oriented partridge management in France. Biological Conservation, 11, 185-191
- Baines D. (1996) The implications of grazing and predator management on the habitats and breeding success of black grouse Tetrao tetrix. Journal of Applied Ecology, 33, 54-62
- Tapper S.C., Potts G.R. & Brockless M.H. (1996) The effect of an experimental reduction in predation pressure on the breeding success and population density of grey partridges Perdix perdix. Journal of Applied Ecology, 33, 965-978
- Summer R.W., Green R.E., Proctor R., Dugan D., Lambie D., Moncrieff R., Moss R. & Baines D. (2004) An experimental study of the effects of predation on the breeding productivity of capercaillie and black grouse. Journal of Applied Ecology, 41, 513-525
- Aebischer N.J. & Ewald J.A. (2010) Grey Partridge Perdix perdix in the UK: recovery status, set-aside and shooting. Ibis, 152, 530-542