Sage Grouse - Preferred Habitat

Preferred Habitat

Sage grouse are totally dependent on sagebrush-dominated habitats. Sagebrush is a crucial component of their diet year-round, and sage grouse select sagebrush almost exclusively for cover. Because sage-grouse habitat and cover requirements are inseparably tied to sagebrush, they will be discussed together.

Breeding: Open areas such as swales, irrigated fields, meadows, burns, roadsides, and areas with low, sparse sagebrush cover are used as leks. Of 45 leks, Patterson reported that 11 were on windswept ridges or exposed knolls, 10 were in flat sagebrush, 7 were in bare openings, and the remaining 17 were on various other site types. Leks are usually surrounded by areas with 20 to 50% sagebrush cover, with sagebrush no more than 1 foot (30.5 cm) tall.

When not on the lek, sage-grouse disperse to the surrounding areas. Wallestad and Schladweiler studied habitat selection of male greater sage grouse in central Montana during breeding season and recorded sagebrush height and canopy cover at 110 daytime feeding and loafing sites of cocks. Eighty percent of the locations occurred in sagebrush with a canopy cover of 20–50%. In another Montana study, sagebrush cover averaged 30% on a cock-use area, and no cocks were observed in areas of less than 10% canopy cover.

Some females probably travel between leks. In Mono County, California, the home range of marked female greater sage grouse during one month of the breeding season was 750 to 875 acres (300–350 ha), enough area to include several active leks.

Nesting: Within a week to ten days following breeding, the hen builds a nest in the vicinity of the lek. Hens usually nest near the lekking grounds, but some hens have been noted to fly as far as 12 to 20 miles (19–32 km) to favorable nesting sites.

Quality of nesting habitat surrounding the lek is the single most important factor in population success. Adequacy of cover is critical for nesting. There can be too little: where 13% was the average percent total crown cover on Idaho range, nests were located where average cover was 17%. No greater sage-grouse hens nested in the most arid, open areas with less than 10% total shrub cover. There can be too much: average shrub cover at 87 nest sites was 18.4%, and in more dense cover, sage-grouse did not nest where total shrub cover was greater than 25%. In Utah no nests occurred where threetip sagebrush cover exceeded 35%.

Sagebrush forms the nesting cover for most sage-grouse nests throughout the West with concealment being the basic requirement. Rabbitbrush (Chrysothamnus spp.) is occasionally used for nesting cover with greasewood (Sarcobatus vermiculatus) and shadscale (Atriplex canescens) being rarely used.

Sage grouse prefer relatively tall sagebrush with an open canopy for nesting. In Utah, 33% of 161 nests were under silver sagebrush that was 14 to 25 inches (36–63.5 cm) tall, while big sagebrush of the same height accounted for 24% of nests. In a threetip sagebrush (A. tripartata) habitat averaging 8 inches (20 cm) in height, hens selected the tallest plants for nesting cover. Similarly, Patterson reported that in Wyoming, 92% of greater sage-grouse nests in Wyoming big sagebrush were in areas where vegetation was 10 to 20 inches (25–51 cm) tall and cover did not exceed 50%.

In Montana, Wallestad and Pyrah compared sagebrush characteristics around 31 successful and 10 unsuccessful nests. Successful nests had greater than average sagebrush cover surrounding the nest and were located in stands with a higher average canopy cover (27%) than unsuccessful nests (20%). Difference was significant at the 0.005 level. They also found the average height of sagebrush cover over all nests was 15.9 inches (40.4 cm) as compared to an average height of 9.2 inches (23.4) cm in adjacent areas (significant at 0.005 level).

During the nesting season, cocks and hens without nests use "relatively open" areas for feeding, and roost in "dense" patches of sagebrush.

Brood rearing: Sagebrush is an essential part of sage grouse brood habitat. An interspersion of sagebrush densities, from scattered to dense, are utilized by broods throughout the summer. Broods can be grouped into two categories: those that remain in sagebrush types through the summer and those that shift from sagebrush types in mid-summer and later return to sagebrush.

Throughout the summers of 1968–1969 in a study in Montana, areas that received the greatest amount of utilization by greater sage-grouse broods were areas of sagebrush density characterized as scattered (1–10%) and common (10–25%). Scattered sagebrush received heaviest utilization in June. "Common" sagebrush was utilized heavily throughout the summer. "Dense" sagebrush had greatest use during late August and early September; "rare" sagebrush cover received greatest use in July and August.

Combined data for both years of the study at brood sites showed an average sagebrush cover of 14% during June, 12% during July, 10% during August and 21% during September, which reflects the vegetational types utilized by broods during the summer. Height of sagebrush at brood sites ranged mainly between 6 to 18 inches (15.2–45.7 cm). In 158 Montana locations, young greater sage-grouse broods used areas of low plant height 9 to 15 inches (23–38 cm)) and density, while older broods and adults used areas where plants were taller (7 to 25 inches (18–63.5 cm).

Early in summer the size of the area used by greater sage-grouse hens with broods in Idaho seemed to depend upon the interspersion of sagebrush types that provided an adequate amount of food and cover. Areas with sagebrush in scattered densities, with occasional clumps in the common to dense categories, appeared to be preferred. In their daily activity, broods tended to use more open sites for feeding and to seek more dense clumps of sagebrush for roosting.

Cover types used by hens with broods typically had greater availability of forbs during periods of high use, but differences in availability between areas influenced use of cover types, movements, and diets.

In Oregon, the greater sage-grouse hens at Jackass Creek selectively used sites with forb cover greater than typically found there and similar to that generally available to broods at Hart Mountain National Antelope Refuge. This amount of forb cover (12–14%) may represent the minimum needed for greater sage-grouse brood habitat in Oregon.

Succulence of their favored foods appears to be a key to sage-grouse movements. As plants mature and dry, the grouse move to areas still supporting succulent vegetation. A delay in maturing of forbs has a noticeable effect on bird movements.

Broodless: A study by Gregg and others in Oregon revealed differences in chronology of summer movements and cover types used between broodless greater sage-grouse hens and greater sage-grouse hens with broods. Broodless hens gathered in flocks and remained separate from but in the vicinity of hens with broods during early summer. However, broodless hens moved to meadows earlier in summer and used a greater diversity of cover types than hens with broods perhaps because dietary needs of broodless hens might be less specific than those of hens with broods.

A winter-use area appears to be both a key habitat segment and a major factor in sage-grouse distribution over a large area. The best winter habitat is below snowline, where sagebrush is available all winter. Dalke and others reported wintering grounds of greater sage-grouse in Idaho were usually where snow accumulation was less than 6 inches (15 cm). In areas of deep snow, greater sage-grouse winter where sagebrush has grown above the snow level.

Sage-grouse appear to select areas of little or no slope. In a Colorado study, nearly 80% of Gunnison sage-grouse winter use of 500 square miles (1,252 km²) of sagebrush was on less than 35 square miles (87 km²): on flat areas where sagebrush projected above the snow, or on south- or west-facing sites of less than 5% slope, where sagebrush was sometimes quite short but still accessible. In Montana, prime wintering areas were flat, large expanses of dense sagebrush; winter home ranges of 5 greater sage-grouse females in Montana varied from 2,615 to 7,760 acres (1,050–3,100 ha) during 2 different years.

Winter-use areas are determined by amount of snow rather than affinity to a particular site. Majority of winter observations are in sagebrush with more than 20% canopy coverage. Species and subspecies of sagebrush that seem to be preferred by grouse in the winter are black sagebrush, low sagebrush, and some subspecies of big sagebrush.