Introduction
Sage grouse (Centrocercus urophasianus) are considered a sagebrush "obligate," even though a portion of their life cycle is associated with meadows. In other words, they require sagebrush (Artemisia sp.) for their existence. More specifically, sagebrush is the major component of sage grouse habitat, providing food, shelter, and nesting cover.
Within the sagebrush habitat type, sage grouse occur at low densities and are distributed unevenly. They may be locally abundant on a seasonal basis. Most of their preferred habitat is found in low rolling hills and adjacent valleys. Optional habitat is a diverse mosaic of sagebrushgrass with varying heights of sagebrush and a diverse understory of perennial grasses and forbs (broadleaf herbaceous plants). The proportion of sagebrush, perennial grasses, and forbs in an area vary with the species or subspecies of sagebrush, the ecological potential of the site, and condition of the habitat.
Sage grouse require the use of sagebrushgrass habitats yearlong; however, the species composition and structural complexity of the habitats used depend on the bird's seasonal requirements. The spatial arrangement, size, and vegetation conditions of each seasonal habitat determine the landscape's suitability for sage grouse. Large, old stands of sagebrush may lack the grasses and forbs that grouse need for food and cover. The use of sagebrush habitats and other habitats by sage grouse is discussed below.
Breeding Habitats (Leks)
Sage grouse "leks" or breeding display sites occur in open areas surrounded by sagebrush. Also called "strutting grounds," these sites are often located in low sagebrush areas, ridgetops, grassy openings, and disturbed areas like burns. This preference for using sparsely vegetated sites for strutting has also resulted in the use of such altered habitats as airstrips, gravel pits, cultivated fields, and roads. Breeding habitats are very traditional, being used year after year, and are considered to be the center of year-round activity for resident grouse populations. However, this is not the case for migratory populations.
Breeding displays on the leks typically begin in March or April. Males display on these sites in gatherings of a few to a few hundred birds.
Breeding occurs in these areas as females are attracted by the strutting displays. The sagebrush habitat surrounding these leks is used extensively by grouse for escape cover, protection from predators, feeding, and loafing. The sagebrush in these adjacent areas is typically 7 to 15 inches tall and has a canopy cover of 20 to 50 percent.
Pre-Nesting and Nesting Habitats
Areas used by pre- laying hens are critical for chick survival. These areas must provide a diversity of forbs so that the hens have a food source high in calcium, phosphorus, and protein, all critical to the hen's nutrition. Without proper and sufficient nutrients, reductions in nesting rates, number of eggs (clutch size), hatching success, and chick survival may occur. A mosaic of good condition low sagebrush (Artemisia arbuscula) and big sagebrush (A. tridentata) typically provides the forbs needed by the hens during this time. The low sagebrush sites are especially important in terms of forb production. Species such as hawksbeard (Crepis sp.), long-leaf phlox (Phlox longiloba), dandelion (Taraxacum officinale), clover (Trifolium sp.), and milk-vetch (Astragalus sp.), are among those preferred by grouse during this time.
After breeding, hens leave the leks to seek suitable nesting habitat. Although the females often nest fairly close to the leks, nesting habitat may be several miles away. Location of nesting areas is a function of the availability of quality habitat. Suitable nesting habitat is typically Wyoming big sagebrush (Artemisia tridentata wyomingensis), communities with 15 to 38 percent sagebrush canopy cover and a grass and forb understory. The hens nest in a shallow depression on the ground, usually under big sagebrush with grasses or other vegetation providing concealment. Although shrub heights at nest sites are variable, sage grouse tend to nest under shrubs taller than the average shrub height in a given area. Those shrubs that provide an "umbrella effect" are preferred. Umbrella-shaped canopies have branches near the ground, while treeshaped shrubs have large open areas between the ground and lower branches.
The amount of grass cover required at sage grouse nest sites is variable, ranging from 3 to 30% cover at successful nest sites. Several studies have shown that grass height and density is greater at nest sites than at random sites. An Oregon study showed less predation on nests in areas where shrubs were 16 to 32 inches tall and residual grass height was at least 7 inches. However, the relative amount of grass required by sage grouse hens at nest sites may also be a function of shrub shape. Where the "umbrella effect" of shrubs is sufficient, residual grass cover may not provide much additional protection from predators. On the other hand, nest sites with more grass cover provide a warmer microclimate for eggs than those with less cover.
Early Brood-Rearing Habitats
Young sage grouse (broods) have higher survival rates when certain food and cover requirements are met. Insects and forbs are the most important food items during the chicks' first month of life. Early brood-rearing areas typically occur in upland sagebrush habitats close to nest sites, although some broods may move to more distant areas at this time.
Optimal early brood-rearing habitat has sagebrush stands that are 16 to 32 inches tall, with a canopy cover of 10 to 25%. The herbaceous understories have approximately 15% grass cover and 10% forb cover. Ideally, this preferred habitat would be found on at least 40% of the area used by sage grouse broods during June and early July. However, composition and structure of the vegetation on any site is a function of the specific plant species and soil types found in the vicinity. Hens with broods tend to select areas during this time that have a wide diversity of plant species and a corresponding diversity of insects.
Late Brood-Rearing Habitats
As food plants mature and dry during mid- July through August, grouse move to areas that support succulent herbaceous vegetation, usually native or irrigated meadows. In general, a mosaic of sagebrush habitats containing grass and forbs, along with interspersed wet meadow areas, form optimum late brood-rearing habitats. Where alfalfa fields and croplands are adjacent to sagebrush habitats, they may be used by grouse during this time of year.
Upland sage grouse habitat in Nevada is drier than that in most western states; therefore the meadow areas are even more important as late summer brood habitat. From mid to late summer, narrow meadows in drainages as well as irrigated hay fields often provide the highest forb abundance for young birds. During drought years, these remaining green areas are even more important for young sage grouse.
Fall Habitats
As the brood groups disperse in early fall, sage grouse form flocks and use a variety of habitats. During this time both frost and the drying of vegetation results in reduc ed forb quality in meadow habitats. As the vegetation dries in late summer and early fall, sage grouse increase their consumption of sagebrush leaves and buds. In some years, grouse may use their summer range as late as October. In other years, sage grouse begin moving to wintering areas by the first week in October. Good fall sage grouse habitat, like other seasonal habitat, is comprised of a mosaic of sagebrush communities with diverse species, varying cover composition, and different height classes.
Winter Habitats
Winter habitat for sage grouse varies according to weather conditions. But regardless of weather, the presence of sagebrush for food and cover is the common denominator. Sage grouse feed almost exclusively on sagebrush leaves at this time of year. At least 10 to 12 inches of sagebrush must be exposed above the snow to allow feeding by sage grouse. Although big sagebrush dominates sage grouse diets in most portions of this bird's range, other sagebrush species are also eaten. In northern Nevada, low sagebrush is used until it is covered with snow, at which time the birds move to big sagebrush areas.
Sagebrush is also important in winter for cover. Sage grouse will roost in open, low sagebrush sites on clear, calm nights above 10°F. However, on windy nights or during snowstorms the birds seek out taller shrubs in areas with 20% or more canopy cover. On cold nights when powdery snow is available, sage grouse will burrow in the snow to conserve energy. These birds will fly more than 5 miles between winter-feeding and snow roosting sites during very cold weather (below 10°F).
Summary
Sage grouse require sagebrush for food and/or cover during each stage of their life cycle and therefore are called "sagebrush obligates." However, sage grouse use other habitats, like wet meadow areas, and increase their dependence on these habitats in mid to late summer during drought years. Although sage grouse depend on the sagebrush habitat type for survival, they thrive best in areas with a mosaic of sagebrush species, age (height), and cover classes.
Selected References
Autenrieth, R.E. 1981. Sage grouse management in Idaho. Idaho Department of Fish and Game Wildl. Bull. 9. Back, G.N., M.R. Barrington, and J.K. McAdoo. 1987. Sage grouse use of snow burrows in northeastern Nevada. Wilson Bull. 99:488- 490. Barnett, J.F., and J.A. Crawford. 1994. Prelaying nutrition of sage grouse hens in Oregon. J. Range Manage. 47:114-118. Barrington, M.R., and G.N. Back. 1984. Sage grouse research; population dynamics. P 43-46. In: P.C. Lent and R.E. Eckert, Jr. (eds.). Progress report for 1983 Saval Ranch Research and Evaluation Project. Univ. Nevada Reno, Renewable Resource Center, Reno, NV. Beck, T.D.I., and C.E. Braun. 1978. Weights of Colorado sage grouse. Condor. 80:241-243. Connelly, J.W., R.A. Fischer, A.D., K.P. Reese, and W.L. Wakkinen. 1993. Renesting of sage grouse in southeastern Idaho. Condor 95:1041-k1043. Connelly, J.W., M.A. Schroeder, A.R. Sands, and C.E. Braun. 2000. Guidelines to manage sage grouse populations and their habitats. Wildl. Soc. Bull. 28:967-985. Gredd, M.A., J.A. Crawford, M.S. Drut, and A.K. DeLong. 1994. Vegetation cover and predation of sage grouse nests in Oregon. J. Wildl. Manage. 58:162-166. Hupp, J.W., and C.E. Braun. 1989. Topographic distribution of sage grouse foraging in winter. J. Wildl. Manage. 53:823-829. Klebenow, D.A. 1969. Sage grouse nesting and brood habitat in Idaho. J. Wildl. Manage. 33:649-661. Klebenow, D.A. 1982. Livestock grazing interactions with sage grouse. Proc. Wildlife-Livestock Relationships Symp., Coeur d'Alene, Idaho. Univ. Idaho, Moscow. pp. 113-123. Klebenow, D.A. 1985. Habitat management for sage grouse in Nevada. World Pheasant Assoc. 10:36-46. Klebenow, D.A. (In Press). Enhancing sage grouse habitat…a Nevada landowners guide. Nev. Wildl. Fed. Pub. Klebenow, D.A., and G.M. Gray. 1968. Food habits of juvenile sage grouse. J. Range Manage. 21:80-83. McAdoo, J.K., and G.N. Back. 2001. Sage grouse biology. Univ. of Nevada Coop. Extension Fact Sheet 01-43. 5pp. Patterson, R.L. 1952. The Sage Grouse in Wyoming. Sage Books, Inc., Denver, Co. Remington, T.E., and C.E. Braun. 1985. Sage grouse food selection in winter, North Park, Colorado. J. Wildl. Manage. 49:1055-1061. Schroeder, M.A., J.R. Young, and C.E. Braun. 1999. Sage grouse (Centrocercus urophasianus). In: The Birds of North America No. 425, (A. Poole and F. Gill, eds). The Birds of North America, Inc., Philadelphia, PA. Sveum, C.M., J.A. Crawford, and W.D. Edge. 1998. Use and selection of brood-rearing habitat by sage grouse in southcentral Washington. Great Basin Nat. 58:344-351. Wallestad, R.O. 1971. Summer movements and habitat use by sage grouse broods in central Montana. J. Wildl. Manage. 35:129-136. Wallestad. R.O., and D. Pyrah. 1974. Movement and nesting of sage grouse hens in central Montana. J. Wildl. Manage. 38:630-633. Welch, B.L., J.C. Pederson, and R.L. Rodriquez. 1988. Selection of sage grouse for big sagebrush. J. Range Manage. 44:462-465.
