Sage Grouse - Food Habits

Food Habits

Adults: The importance of sagebrush in the diet of adult sage-grouse is impossible to overestimate. Numerous studies have documented its year-round use by sage-grouse. A Montana study, based on 299 crop samples, showed that 62% of total food volume of the year was sagebrush. Between December and February it was the only food item found in all crops. Only between June and September did sagebrush constitute less than 60% of the greater sage-grouse diet. Sage-grouse select sagebrush species differentially. Greater sage-grouse in Antelope Valley, California, browsed black sagebrush more frequently than the more common big sagebrush. Young and Palmquist state the browse of black sagebrush is highly preferred by greater sage-grouse in Nevada. In southeastern Idaho, black sagebrush was preferred as forage.

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. 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 dubius), western yarrow (Achillea millefolium), prickly lettuce (Lactuca serriola) and sego lily (Calochortus macrocarpus).

Juveniles: In their first 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.

A Wyoming study evaluated effects of eliminating insects from the diet of newly-hatched 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 first ten days. Captive greater sage-grouse chicks required insects for survival until they were at least three weeks old. Greater sage-grouse chicks more than three weeks old survived without insects, but their growth rates were lowered significantly, indicating insects were still required for normal growth after three 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 (Leptosiphon 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.

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.

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.