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

Abstract

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. J. WILDL. MANAGE. 51(1):167-172 Capercaillie and black grouse are lekking species. The cryptically colored females nest solitarily on the ground at varying distances from the lek (Bernard 1982, Wegge et al. 1982a, Kolstad et al. 1985), and the 2 species differ in general habitat selection. Most of the year, black grouse use younger forest successional stages and open moorland habitats, whereas capercaillie select mature climax forests (Seiskari 1962, Borset and Krafft 1973, Wegge et al. 1982b, Angelstam 1983). Boreal forests in Norway are exploited for commercial logging, which since the 1950's has been characterized by clearcuts of 6-20 ha, subsequently replanted to monocultures of Norway spruce (Picea abies) or Scotch pine (Pinus sylvestris). Nest losses, particularly in capercaillie, seem to have increased in recent years, estimated at 64-83% in the area of this investigation (Storaas and Wegge 1985). The nesting habitats of black grouse have been studied by Bernard (1982) in the French Alps. However, except for some superficial notes (H6glund 1953, Siivonen 1953, Semenow-TjanSanskij 1960) and observations in Scottish plantations (Jones 1985), no systematic study has been published on the nesting habitats of capercaillie. The aim of this paper is to compare the nest sites of sympatric populations of caperca llie and black grouse, to relate the fate of nests to habitat types, habitat density, and nest cover, and to discuss the factors affecting nest site selection. The study was financed by the Norwegian Dir. Nat. Conserv. and the T. Gotaas Fund. O. Bakken, I. Gjerde, A. Haugland, L. Kastdalen, B. B. Larsen, M. Ribsskog, and J. Rolstad assisted in the field. F. C. Zwickel and B. W. O'Gara gave valuable comments on the manu-