Nesting Habitats and Nest Predation in Sympatric Populations of Capercaillie and Black Grouse

During 1979-85, 196 capercaillie (Tetrao urogallus) and 90 black grouse (T. tetrix) nests were studied at Varaldskogen in southeast Norway. Both species nested in all available habitat types and in a wide range of forest tree-stocking density and nesting cover. Both species preferred to nest in the habitat types to which they are generally adapted, capercaillie in mature, mixed coniferous forest and black grouse in forested bogs. Black grouse used denser nest cover than capercaillie. Individually marked capercaillie females changed successive nesting habitats 12 of 19 (63%) possible times. Nest loss was unrelated to habitat type, forest density, or nest cover. Capercaillie suffered higher nest loss than black grouse in all comparable habitats. Depredated eggs of both species composed about 10% of the food demands of predators. Because nests survived equally well in all habitats and no single predator depended on grouse eggs for food, there may be no selection for rigid nest-site characteristics. High nest predation in recent years cannot be ascribed to direct effects of modern forestry on nesting habitats.