Species Profile: Gunnison Sage-Grouse

Photo: Wendy Shattil/Bob Rozinski

One of the most recent species recognized by the American Ornithologist’s Union is the Gunnison Sage-Grouse (Centrocercus minimus). Accepted as a new species in July 2000, it had been overlooked by both conservationists and taxonomists for nearly 200 years and was originally thougth to differ from the Greater Sage-Grouse (Centrocercus urophasianus) in size only. Several studies of this species during the last decade, however, have noted its distinctive breeding plumage and vocalizations, as well as behavioral and genetic differences, that separates it from the more common Greater Sage-Grouse. A large white throat pouch, greenish-yellow air sacs, long pointed tail feathers, and thick filoplumes on the nape of the head separate the 4-5 pound male from the smaller female during the breeding season.

Gunnison Sage-Grouse are a sagebrush obligate, and depend upon big sagebrush as a principal food and as habitat for nesting, roosting, and brood-rearing. Their primary habitat consists of large expanses of sagebrush on flat or gently rolling terrain at elevations of 7,500 to 9,500 feet, with wet meadows and riparian areas being used as brood habitat in summer. The Gunnison Sage-Grouse, historically found in Colorado, Utah, New Mexico, and Arizona, is now restricted to six or seven counties in southwestern Colorado and one county in southeastern Utah. Current range wide populations are estimated at 4,000 to 5,000 individuals, with most occurring in Gunnison County, Colorado.

The spectacular breeding displays of sage grouse, often called “Cock of the Plains” are reflected in dances of western Native Americans and have fascinated generations of naturalists, ecologists, photographers, and hunters. Each spring male Gunnison Sage-Grouse gather before sunrise on traditional display grounds called “strutting grounds” to assert their dominance over other males nad compete for the attention of females. Usually 20 to 50 or more males attend each strutting ground from March through May and display vigorously to defend their territories from other males and to attract females. Sage grouse have a polygamous mating system in which a few older and more dominant males are successful in breeding all females.

Males initiate their ritualized strutting display by taking a few steps forward as wings are raised and lowered and brushed twice against the stiff white throat pouch, producing swishing noises. The display is continued as they expand their greenish-yellow air sacs and pop them several times in rapid succession. Under calm conditions, these sounds can be heard 1-2 miles away. Males conclude the strutting display by throwing their filoplumes over their head and wagging their tail. The entire display lasts only three seconds and is usually repeated dozens of times each hour, especially when females are present. At territory boundaries males often face each other while clucking rapidly and occasionally beat each other with their wings. Display slows down a few hours after sunrise with males and any remaining females flying up to half a mile away to spend the day feeding and resting. Males often display at dusk, especially early in the breeding season, when females in the vicinity of leks stimulate strutting behavior.

After breeding in early April, hens disperse for nesting, with most nests being within 3 miles of the strutting ground. Nests are simple scrapes in the ground, typically at the base of a large sagebrush shrub, and hidden by forbs and grasses. Clutches average 7-9 eggs which usually hatch in mid-June after a 27-28 day incubation period. Chicks are precocial and leave the nest within a day of hatch. Hens and broods feed upon a variety of insects and succulent forbs until mid-September.

Movements of males and females in late-fall and early winter can be quite extensive, as birds seek stands of tall sagebrush, whose leaves comprise their most important food until the following summer. During periods of extreme cold and snow, birds will spend nights and portions of the day, when not foraging, in snow roosts, where the microclimate is more tolerable. Winter flocks are often comprised primarily of one gender, with flocks of females averaging more birds than male flocks.

Because sage grouse are considered a game species, state wildlife agencies have monitored populations using counts of displaying males on active strutting grounds. Populations have fluctuated markedly over the years, with a long-term downward trend. The decline in Gunnison Sage-Grouse populations is attributed to loss of sage-brush habitats from urban and rural development, land conversion to hay meadows and cropland, encroachment of pinon-juniper forests, and habitat fragmentation from roads, power lines, reservoirs and development. Loss of corridors between populations has resulted in loss of genetic diversity in isolated populations.