Description
The sage grouse (Centrocercus urophasianus) is one of seven species of grouse (Family Phasianidae) in North America and is also called the northern or greater sage grouse. First described in writing by Lewis and Clark during their 1805 expedition, this bird is often referred to as sage hen, sage cock, or sage chicken. Sage grouse are the largest North American grouse species, with males ranging from 27 to 34 inches in length and weigh 5 to 7 pounds, while females are 18 to 24 inches in length and weigh 2 to 3 pounds. They are grayish-brown birds with dark bellies and long, pointed tail feathers. As with all grouse, the feet are feathered to the toes on both sexes. Recent DNA work has identified a small distinct population in southwest Colorado as a separate species, the Gunnison sage grouse (C. Minimus). Another population, in the White Mountains on the Nevada/California border, may also be different from the greater sage grouse and is currently being genetically evaluated.
Distribution
Sage grouse were historically found throughout most of the western United States, including portions of 16 states and along the southern border of three western Canadian provinces. This distribution closely parallels the range of sagebrush (Artemisia sp.) communities. The current core of sage grouse populations includes areas of Colorado, Idaho, Montana, Nevada, Oregon, and Wyoming, with remnant populations in other states. Within Nevada, sage grouse distribution is associated with sagebrush habitat in the northern two-thirds of the state (Fig. 1). The northeastern block of counties provides the most continuous sage grouse habitat. Although sage grouse numbers in the state are currently unknown, trend counts indicate that the statewide population has been declining since 1979.
Breeding and Reproduction
Sage grouse have a "lek" mating system. This involves the males performing "strutting" displays on typically the same or traditional leks (strutting grounds) year after year. During this display, the cocks fan their tail feathers in an upright fashion, exposing white-tipped under tail feathers. They also expand pouches on their necks that expose yellow skin patches. This pouch expansion produces a series of "plop" noises. Accompanied by movements and postures, this display is an active defense of the breeding territory by each male. As females are attracted to the lek area, only a few males on each lek do the majority of the mating.
Sage grouse breeding begins in approximately mid-March, when the males start to congregate on the leks. After coming to the leks to mate, the females nest in the general vicinity of the leks, depending on the availability of suitable habitat. Most nesting occurs within 4 miles of leks, but sites have been reported as far as 12 miles away from the leks.
Nesting rates and nest success varies from year to year and by area, most likely the result of nutrition quality, health of the pre-laying hens, and habitat structure. Typically, at least 70% of the hens in a population will initiate nesting each year. More hens nest during years of higher precipitation, as compared to drought years. Only 10 to 40 percent of females who have lost their first clutch (nest of eggs) attempt to re-nest. In terms of nest success, from 10 to 86% of nesting hens will produce chicks. Adult females have higher nesting success rates than yearling females.
Size of the clutch is variable and relatively low as compared to other game bird species, normally averaging 7 to 10 eggs. Once again, nutrition quality and condition of the pre-laying hens probably affects clutch size.
Movements and Migration
Throughout their range, sage grouse populations can be either migratory or nonmigratory, depending on site-specific conditions. In areas where elevation varies, the non-migratory or "resident" birds typically move up in elevation from spring through fall in response to snow melt and vegetation green-up. The degree of movement among seasonal ranges by resident birds is variable and depends on habitat quality and distribution, weather, and even gender and behavioral differences among birds. Movement of resident young birds (broods) from nesting areas to summer habitat is related directly to insect availability and the drying up of forbs (broadleaf herbaceous plants), the preferred food sources at this time. The movement of birds to fall and winter range is also related to food quality, with grouse increasing their consumption of sagebrush at this time. Movements made during winter are similarly related to food quality and availability, as well as snow depths. Some birds may even move on to nesting areas during mild weather conditions. Even with these seasonal movements, non-migratory sage grouse populations will typically spend an entire year within an area of 39 square miles or less.
In contrast, migratory grouse populations may travel more than 47 miles between seasonal ranges and have home ranges that exceed 580 square miles. The migratory populations can be further defined as one-stage migratory (birds that move between two distinct seasonal ranges) and two-stage migratory (birds that move among three distinct seasonal ranges). Seasonal ranges, may include a breeding range, brood-rearing range, and/or winter range. This indicates that sage grouse can require large expanses of habitat. Migratory movements of grouse are probably triggered by the same factors that stimulate seasonal movements in resident populations. Interestingly, migratory and resident populations sometimes share certain seasonal habitats.
The Nevada Division of Wildlife has confirmed through tracking of radio-collared birds that specific Nevada sage grouse populations might be either resident or migratory. The extent of seasonal movements and migration can vary substantially within and among grouse populations. Some Nevada grouse do not migrate, wintering on the breeding grounds. Other populations migrate after the breeding season, spending the summer and fall up to 40 miles from the breeding area. These populations then return to the breeding area to winter. Still other populations separate, then migrate up to 20 miles to two different wintering grounds.
Food Habits
The annual diet of sage grouse is comprised of sagebrush, grasses, forbs, and insects. Because sage grouse are the only North American grouse species that does not have a muscular grinding gizzard, these birds cannot digest hard foods such as seeds. This limits the diet of sage grouse to soft plant parts and insects.
During the course of a year, sagebrush is quantitatively the most important component in the diet of sage grouse, comprising 60 to 80% of all food consumed. However, seasonally, other food sources are extremely important. For example, during spring and summer, these birds shift from a sagebrush-dominated diet to one of forbs, grasses, and insects. Forbs and grasses are important to hens during the pre-laying period and comprise more than half of the juvenile diet until the broods are approximately three months old. Although sage grouse will consume many forb varieties, some of the more important species include common dandelion (Taraxacum officinale), clover (Trifolium sp.), common salsify (Tragopogon dubius), prickly lettuce (Lactuca serriola), hawksbeard (Crepis sp.), pepperweed (Lepidium densiflorum), gilia (Gilia sp.), phlox (Phlox longifolia), milkvetch (Astragalus sp.), and western yarrow (Achillea millefolium). Sagebrush is a very minor component in the diet of grouse chicks until they are about five weeks old. Insects, especially ants (Hymenoptera), beetles (Coleoptera), and grasshoppers (Orthoptera) are critically important in the diet of chicks during their first weeks of life.
Insects may comprise more than 50% of grouse chicks' diet during their first two weeks. Young birds up to three weeks old require approximately 15 grams of insects daily. Older chicks can survive without insects, but have reduced growth rates if insects are completely absent from their diet. The species of insects consumed by young grouse varies with age of the chicks, but may also be a function of the exact habitats used and life stages of the insects. Although insects comprise the greatest proportion of food in young chicks' diets, the percentage of insects declines as the percentage of plant material (especially forbs) increases.
Although the summer food habits of adult sage grouse are similar to those of juveniles, there are differences in the proportions consumed. Adult grouse will consume insects when they are available, but plant material makes up a larger proportion of the adult diets from early to mid-summer. However, qualitatively, the specific food items eaten by adults are very similar to those chosen by the juveniles.
Sage grouse consumption of sagebrush increases during late summer, and sagebrush becomes the major food item during fall and winter. The species of sagebrush used as food by sage grouse includes Wyoming big sagebrush (Artemesia tridentata wyomingensis), mountain big sagebrush (A.t. vaseyana), low sagebrush (A. arbuscula), black sagebrush (A. nova), fringed sagebrush (A. frigida), and silver sagebrush (A. cana). Sage grouse are one of the few wildlife species that actually maintain or gain fat and weight during cold, snowy winters. This is made possible by their ability to select plant species and perhaps even specific plants with high levels of protein and energy.
Life Span and Mortality Rates
In both hunted and protected populations, average life span of sage grouse is 1 to 1.5 years, with 3- to 4-year old grouse considered old. Annual survival rates for yearling and adult females varies from 35 to 85%, with male survival rates ranging from 38 to 54%. The lower survival rates of males may be related to higher predation rates on males during the mating season when they spend more time in open areas. The stability of a sage grouse population is a function of clutch size, nest success, chick survival, and adult survival. Research has shown that maintenance of stable to increasing sage grouse populations requires at least 2.25 juveniles per hen surviving until the fall.
Selected References
Beck, T.D.I. 1977. Sage grouse flock characteristics and habitat selection in winter. J. Wildl. Manage. 41:18-26. Berry, J.D., and R.L. Eng. 1985. Interseasonal movements and fidelity to seasonal use areas by female sage grouse. J. Wildl. Manage. 49:237-240. Connelly, J.W., H.W. Browers, and R.J. Gates. 1988. Seasonal movements of sage grouse in southeastern Idaho. J. Wildl. Manage. 55:521-524. Dalke, P.D. 1963. Ecology, productivity, and management of sage grouse in Idaho. J. Wildl. Manage. 27:811-841. Gregg, M.A., J.A. Crawford, M.S. Drut, and A.K. DeLong. 1994. Vegetational cover and predation of sage grouse nests in Oregon. J. Wildl. Manage. 58:162-166. Klebenow, D.A. 1985. Habitat management for sage grouse in Nevada. World Pheasant Assoc. 10:36-46. 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 habitat requirements. Univ. of Nevada Coop. Extension Fact Sheet 01- 44. 4pp. Peterson, J.G. 1970. The food habits and summer distribution of juvenile sage grouse in central Montana. J. Wildl. Manage. 34:147-155. 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. Scott, J.W. 1942. Mating behavior of the sage grouse. Auk 59:477-498. Wakkinen, W.L., K.P. Reese, and J.W. Connolly. 1992. Sage grouse nest location in relation to leks. J. Wildl. Manage. 56:381-383. 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., J.G. Peterson, and R.L. Eng. 1975. Foods of adult sage grouse in central Montana. J. Wildl. Manage. 39:628-630. 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. Rodriguez. 1988. Selection of sage grouse for big sagebrush. J. Range Manage. 44:462-465.
