Habitat
Alpine tundra, especially in rocky areas with sparse vegetation (AOU 1983). Summer habitats in the Rocky Mountains consistently include moist, low-growing alpine vegetation. In Colorado, percent canopy cover of willow was higher at winter feeding sites than at random sites (Giesen and Braun 1992). In the Sierra Nevada, breeding season habitats were in areas of tall (>30 cm) willow shrubs and contained more subshrub, moss, and boulder cover than in unused habitats; in postbreeding season, used topographic depressions within breeding territories; brooding hens used moist meadows, while flocks occupied sites with abundant boulders; primarily used the Salix anglorum antiplasta vegetation alliance on rocky, north-facing slopes; willow abundance and proximity to water were important habitat factors (Frederick and Gutierrez 1992). Nests in alpine tundra, in rocky areas or sparsely vegetated, grassy slopes. Tends to search for vacant territory in natal area. High fidelity to breeding territory in successive years.
Ecology
Broods stay together in family groups until following spring (Harrison 1978). Sedentary. In the Sierra Nevada, overall density was 4.4-5.7/100 ha in breeding season, 4.7-7.1/100 ha postbreeding; density within occupied habitat was 10.5-14.2/100 ha in breeding season, 21.8-27.7/100 ha postbreeding; number of breeding pairs was 1.8/100 ha and 2.8/100 ha in two areas (Frederick and Gutierrez 1992). Overall breeding density at Logan Pass, Montana, was 6.8/100 ha; density within suitable habitat was 19.3/100 ha; 10.6/100 ha postbreeding. In Colorado, breeding density in three unhunted populations was 9.6-11.9/100 ha; 15.7-23.4 postbreeding (see Frederick and Gutierrez 1992). In Colorado, winter home ranges of 17 females averaged 1.62 sq km (4 of these averaged 2.44 sq km); those of 2 males averaged 0.44 sq km; winter density averaged 10-20 birds/sq km (Giesen and Braun 1992).
Reproduction
Female incubates 4-7, sometimes 3-9, eggs for 22-23 days (Harrison 1978). Nestlings are precocial and downy. Brood size in Sierra Nevada averaged 2.6-2.8; brood size in five areas in Colorado was 3.2-4.5; brood size at flight age in Montana was 3.3-3.5. Young are guarded by both parents, capable of flying in about 10 days. Monogamous. In the Sierra Nevada, reproductive success decreased with increasing spring snow depth (Condor 94:622-627).