Among the big sagebrush subspecies, basin big sagebrush is less nutritious and higher in terpenes than either mountain or Wyoming big sagebrush. Sage-grouse prefer the other two subspecies to basin big sagebrush . In a common garden study done in Utah, Welch, Wagstaff and Robertson  found sage-grouse preferred mountain big sagebrush over Wyoming and basin big sagebrush. However, when leaves and buds of the preferred species became limited, the birds shifted to the lesser-liked plants. The authors concluded the birds, while expressing preference, are capable of shifting their eating habits.
Sage-grouse lack a muscular gizzard and cannot grind and digest seeds; they must consume soft-tissue foods . Apart from sagebrush, the adult sage-grouse diet consists largely of herbaceous leaves, which are utilized primarily in late spring and summer . Additionally, sage-grouse use perennial bunchgrasses for food .
Sage-grouse are highly selective grazers, choosing only a few plant genera. Dandelion (Taraxacum spp.), legumes (Fabaceae), yarrow (Achillea spp.) and wild lettuce (Lactuca spp.) account for most of their forb intake [6,110]. Martin  found that from July to September, dandelion comprised 45% of greater sage-grouse intake; sagebrush comprised 34%. Collectively, dandelion, sagebrush, and two legume genera (Trifolium and Astragalus) contributed more than 90% of the sage-grouse diet. Insects are a minor diet item for adult sage-grouse. Martin and others  reported insects comprised 2% of the adult greater sage-grouse diet in spring and fall and 9% in summer. Sagebrush made up 71% of the year-round diet.
Prelaying females: Herbaceous dicots are used heavily by females before egg laying and may be essential for sage-grouse nutrition because of their high protein and nutrient content .
Favored foods of prelaying and brood-rearing greater sage-grouse hens in Oregon are :
common dandelion (Taraxacum officinale)
goatsbeard (Tragopogon dubuis)
western yarrow (Achillea millifolium)
prickly lettuce (Lactuca serriola)
sego lily (Calcochortus macrocarpus)
In southeastern Oregon, Barnett and Crawford  studied prelaying nutrition of greater sage-grouse hens, March to April, 1990 and 1991.
|frequency of occurrence among crops||relative dry weight|
|big sagebrush 1990 (N = 7) %||low sagebrush 1990 (N = 13) %||low sagebrush 1990 (N = 22) %||big sagebrush 1990 (N = 7) %||low sagebrush 1990 (N = 13) %||low sagebrush 1990 (N = 22) %|
|desert-parsley (Lomatium spp.)||86||92||68||7||16||8|
|hawksbeard (Crepis spp.)||57||62||37||11||14||3|
|long-leaf phlox (Phlox longifolia)||86||92||55||12||4||2|
|mountain dandelion (Agoseris spp.)||28||69||11||2||4||1|
|clover (Trifolium spp.)||0||31||18||0||4||1|
|everlasting (Antennaria spp.)||43||69||41||8||3||2|
|woollypod milk-vetch (Astragalus purshii)||57||31||9||2||<1||<1|
|buckwheat (Eriogonum spp.)||14||8||0||2||<1||0|
|arcane milk-vetch (A. obscurus)||0||31||5||0||2||<1|
|buttercup (Ranunuculus spp.)||0||8||0||0||<1||0|
|other phlox (Phlox spp.)||14||15||18||<1||<1||<1|
|blue-eyed Mary (Collinsia spp.)||0||38||9||0||<1||<1|
|bluebells (Mertensia spp.)||0||0||5||0||0||<1|
|larkspur (Delphinium spp.)||0||0||5||0||0||<1|
|rockcress (Arabis spp.)||14||0||0||<1||0||0|
Juveniles: In their 1st week of life, sage-grouse chicks consume primarily insects, especially ants and beetles . Their diet then switches to forbs, with sagebrush gradually assuming primary importance. In a Utah study, forbs composed 54 to 60% of the summer diet of juvenile sage-grouse, while the diet of adult birds was 39 to 47% forbs .
In a Wyoming study, Johnson and Boyce  evaluated effects of eliminating insects from the diet of newly-hatched greater sage-grouse chicks. All chicks hatched in captivity and not provided insects died between the ages of 4 and 10 days, whereas all chicks fed insects survived the 1st 10 days. Captive greater sage-grouse chicks required insects for survival until they were at least 3 weeks old. Greater sage-grouse chicks > 3 weeks old survived without insects, but their growth rates were lowered significantly, indicating insects were still required for normal growth after 3 weeks of age. As quantity of insects in the diet increased, survival and growth rates also increased up to 45 days, the length of the experiment.
In a study conducted in Idaho, Klebenow and Gray  measured food items for juvenile greater sage-grouse for each age class, classes being defined by weeks since birth. In the 1st week insects were very important - 52% of the total diet. Beetles, primarily family Scarabaeidae, were the main food item. Beetles were taken by all other age classes of chicks, but in smaller amounts. All ages fed upon ants and while the volume was generally low, ants were found in most of the crops. After week 3, insect volume dropped and stayed at a lower level throughout all the age classes, fluctuating but always under 25%.
Forbs were the major plant food of the chicks. Harkness gilia (Linanthus harknessii) was the main forb species in the 1st week and then steadily decreased. It was not found in the diet after 6 weeks. Loco (Arabis convallarius) and common dandelion were important food items for most of the collection period and occurred with generally high frequencies. Common dandelion was the most abundant food item and the mainstay of the sage-grouse chicks. At 6 weeks of age, goatsbeard reached its peak in the diet and sego lily was found in greatest volume a week later. These 5 species were the most important forbs.
The only shrub of importance was big sagebrush. It appeared in the diet at 4 weeks of age and as the ages progressed, the volume increased steadily. These 6 plants comprised 83% of the total sample and are listed in order of decreasing percent total volume :
|food item||part||% of total|
|common dandelion||buds, seeds||80|
|Sego lily||buds, capsules||100|
With plants like common dandelion and goatsbeard, all aboveground parts of the plant were sometimes eaten. The stems, however, were not of main importance. The reproductive parts, mainly buds, flowers, and capsules, were the only parts taken from some of the other species. Conversely, leaves were the only parts of sagebrush found in the crops. Leaves and flowers of the species listed above and other dicots contained higher amounts of crude protein, calcium, and phosphorus than sagebrush and may be important in greater sage-grouse diets for these reasons .
In a central Montana study, Peterson  analyzed crop contents of juvenile greater sage-grouse. Data indicate increasing use of sage species and decreasing use of insects. Percent frequency and percent volume of food items commonly utilized by 1- to 12-week-old greater sage-grouse collected during 1966 and 1968 were:
|1-4 n = 26||5-8 n = 47||9-12 n = 54|
|food item||%Freq/(%Vol)||%Freq /(%Vol)||%Freq /(%Vol)||Total1 % Freq/ (%Vol)|
|curlycup gumweed (Grindelia squarrosa)||9/trace||28/3||39/4||25/2|
|alfalfa (Medicago sativa)||--||21/2||22/2||14/1|
|littlepod false flax (Camelina microcarpa)||9/1||2/trace||--||4/trace|
|skunkbush sumac (Rhus trilobata)||--||3/3||--||1/1|
|wheat (Triticum aestivum)||--||--||9/3||3/1|
|Ttotal volumes of trace material||2||1||1||1|
|TOTAL PERCENT PLANT VOLUME||70||76||83||76|
|TOTAL VOLUMES OF TRACE MATERIAL||8||--||--||3|
|TOTAL PERCENT ANIMAL VOLUME||30||24||17||24|
Five most preferred1 plant species in each 2-week age division of juvenile sage-grouse, 1966 and 1968 are listed below. Note only 1 sagebrush species is listed and that it is not preferred until weeks 7-8 :
|food item||1-2, n=8||3-4, n=8||5-6, n=17||7-8, n=16||9-10 n=11||11-12 n=9||13-14 n=6|
|common pepperweed (Lepidium densiflorum)||4||2||-||-||-||-||-|
|littlepod false flax||-||4||-||-||-||-||-|
|American vetch (Vicia americana)||1||-||-||-||-||-||-|
|Breitung blue lettuce (Lactuca pulchella)||-||-||1||-||-||-||-|
|sedges (Carex spp.)||-||-||-||-||-||-||1|
Water: Sage-grouse apparently do not require open water for day-to-day survival if succulent vegetation is available. They utilize free water if it is available, however. Sage-grouse distribution is apparently seasonally limited by water in some areas. In summer, sage-grouse in desert regions occur only near streams, springs, and water holes. In winter in Eden Valley, Wyoming, sage-grouse have been observed regularly visiting partially frozen streams to drink from holes in the ice .