THE SAGE GROUSE
The greater sage-grouse and Gunnison's sage-grouse have ranges that largely overlap the distribution of big sagebrush, and to a lesser extent silver sagebrush in western North America. Because of range-wide declines in their populations and distribution, there are concerns for their long-term survival. The Gunnison's sage-grouse and greater sage-grouse in are considered to be candidates for federal listing under the Endangered Species Act.
General Description of Species, Subspecies and Related Species: The greater sage-grouse and Gunnison sage-grouse have ranges that originally mirrored the distribution of big sagebrush, and to a lesser extent silver sagebrush, ecosystems in western North America. Because of range-wide declines in their populations and distribution, there are concerns for the long-term survival of both species. The Gunnison sage-grouse and greater sage-grouse are candidates for federal listing under the Endangered Species Act.
General Description and Species Variation: The greater sage-grouse (Centrocercus urophasianus) is the largest grouse in North America. It’s very large size (70-75 cm long, males = 2.7-3.3 kg, females = 1.4-1.9 kg), long pointed tail, and distinctive mottled grey-and-white plumage distinguish the greater sage-grouse from all other North American grouse, other than the Gunnison sage-grouse (Centrocercus minimus). Recently recognized as a distinct species, the Gunnison sage-grouse is similar in appearance but about 30% smaller (males = 1.6-2.4 kg, females = 1.0-1.4 kg) and lighter in color than the greater sage-grouse. In addition, male Gunnison sage-grouse have shorter, more distinctively-barred tail feathers than male greater sage-grouse. Males of both species are larger than the females and possess prominent white upper-breast feathers. During the breeding season, males develop discernible air sacs on the breast and specialized ornamental contour feathers known as filoplumes that arise from the dorsal base of the neck. The filoplumes of male Gunnison sage-grouse are longer and thicker than those of greater sage-grouse males. There are 2 weakly differentiated subspecies of greater sage-grouse.
Diet: Sagebrush leaves dominate the diet of adult sage-grouse throughout the year, and during winter months are essentially the only food ingested. Forbs are consumed by hens during pre-laying and by all age and sex classes during summer. Insects are critical for juveniles during the first 3-4 weeks of life, with forbs increasing in the diet as the young birds age. Insects also are utilized by adults during spring and summer. Of particular note, is the degree to which sage-grouse have adapted to surviving in the sagebrush steppe. For example, sage-grouse are at their physical peak during the breeding season, which is early spring at the end of a bitter winter on the open sagebrush steppe. While most other animals that share this ecosystem with sage-grouse during the winter, such as mule deer and pronghorn, are at their lowest annual fitness levels coming off of winter range, the sage-grouse thrives in the harsh conditions that is a winter on the sagebrush sea.
Breeding Characteristics: Males gather on traditional breeding areas known as leks or strutting grounds where they perform elaborate displays and vocalizations to attract females for breeding. Although, males establish breeding territories on leks as yearlings, yearling males seldom actually breed with females; in fact, only 10-15% of the adult males actually are successful at mating on the lek. Females typically visit the lek only once or twice a year, selecting dominant males for breeding. Male sage-grouse play no part in rearing young.
Nesting Characteristics: The majority of female greater sage-grouse nest within 6 to 7 km from the lek where they were bred, however, some hens have traveled as far as 64 km from the lek for nesting. Sage-grouse are ground nesters and construct their nest under sagebrush plants, typically in areas with dense residual grass cover. No concealment strategies are attempted at the nest except that afforded by natural cover and the hen’s cryptic plumage coloration pattern. Females lay an average of 7-9 eggs that are olive-buff to greenish-brown with small dark brown spots. The incubation period lasts 25-29 days. Nesting success is highly variable, but typically 40-60% of hens will successfully hatch a clutch of eggs. Both adult and yearling hens will attempt to nest, but adults tend to be more successful than yearlings. Sage-grouse generally do not re-nest if the first nest is destroyed.
Brood-Rearing Characteristics: Sage-grouse raise one brood per year. The female grouse provides thermal protection and leads the chicks to sources of food, where they forage on their own. At hatch, the chicks are fully-covered with a dense down plumage, which is supplemented rapidly with flight and body feathers. They can sustain short flights at 10-14 days of age and become independent of the brood hen at 10-12 weeks of age, although chicks tend to spend their first year of life within a mixed flock of brood-rearing females and young-of-the year. Sage-grouse hens with broods often congregate near mesic areas such as stream corridors or irrigated agricultural fields. Some mixing of broods occurs at these sites, and chicks may follow hens that are not their mothers—which results in broods of mixed ages sometimes being observed; this situation should not be confused with multiple broods hatched by one hen.
Habitat Characteristics: As its name implies, sage-grouse are completely tied to the sagebrush ecosystems of western North America; the dependence of the species on sagebrush through all seasonal periods has been well-documented and cannot be over-emphasized. There is tremendous natural variation in sagebrush communities within this ecosystem to which the sage-grouse have adapted. A robust understory of forbs and grasses is required in addition to sagebrush to meet annual needs.
Range: The current range of the greater sage-grouse includes extreme southeast Alberta and southwest Saskatchewan, extreme southwest North Dakota and northwest South Dakota, much of Montana and Wyoming, western Colorado, parts of southern and eastern Idaho, portions of north, northeast and south Utah, northern Nevada, extreme east to northeast California, southeast Oregon, and north-central Washington. Sage-grouse are thought to occur in approximately 56% of their pre-European settlement distribution. Gunnison sage-grouse occur in small isolated populations in southwest Colorado and southeast Utah.
Survival: Although greater sage-grouse congregate on leks and nest on the ground, behaviors that should subject them to higher predation rates, their large size limits the number of predators (especially avian predators) that prey upon them. Thus, greater sage-grouse tend to have higher survival rates than other species of grouse, with females (55-75%) surviving at a higher rate than males (35-60%). However, these relatively high survival rates are combined with relatively low reproductive rates, resulting in populations that do not fluctuate as widely as those of other grouse species.
Population Status: Greater sage-grouse populations across most of their range have been experiencing long-term population declines since the mid-1960s. It has been estimated that the number of sage-grouse in the 1960s and 70s were double or triple current numbers, depending on the region investigated.
Current Problems and Threats: The distribution and abundance of sage-grouse have declined dramatically throughout the range for both species. The Gunnison sage-grouse currently is classified as a "candidate species" and petitions have been filed to list the greater sage-grouse. The primary threats to sage-grouse populations include habitat loss, degradation, and fragmentation due to conversion of native sagebrush communities to croplands and pasture for livestock, excessive livestock grazing that degrades the remaining sagebrush communities, herbicide treatment, invasion of non-native plants and the resulting unnatural fire regimes, and energy development.
Life History Coming Soon!