Individual study: Predator removal increases productivity and adult abundance in tetraonids on two islands in the Gulf of Bothnia, Sweden
Marcstrom V., Kenward R.E. & Engren E. (1988) The Impact of Predation on Boreal Tetraonids During Vole Cycles: An Experimental Study. Journal of Animal Ecology, 57, 859-872
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Control mammalian predators on islands for gamebirds
A replicated, controlled study on two islands (18 km2 and 23.5 km2) in the Gulf of Bothnia, Sweden between 1976 and 1984 (Marcstrom et al. 1988) found that gamebird brood sizes were significantly larger and a higher proportion of females had chicks over a four year period when predators were controlled, compared to when predators were not removed (with predator control: 5.5 chicks/brood, 77% of 378 hens had chicks; without predator control: 3.3 chicks/brood, 59% of 314 hens had chicks). . Species studied were capercaillie Tetrao urogallus, black grouse Tetrao tetrix, hazel grouse Bonasa bonasia and willow ptarmigan Lagopus lagopus, with adult capercaillie and black grouse counts increasing by 56-80% after predators had been controlled for two years, and counts at leks increasing by 166-174%. Predators (European pine martins Martes martes and red foxes Vulpes vulpes) were trapped and shot.