Temporal Variation in Diet and Nutrition of Preincubating Greater Sage-Grouse

Abstract

Greater sage-grouse (Centrocercus urophasianus) habitat management involves vegetation manipulations to increase or decrease specific habitat components. For sage-grouse habitat management to be most effective, an understanding of the functional response of sage-grouse to changes in resource availability is critical. We investigated temporal variation in diet composition and nutrient content (crude protein, calcium, and phosphorus) of foods consumed by preincubating female sage- grouse relative to food supply and age of hen. We collected 86 preincubating female greater sage-grouse at foraging areas during early (18-31 March) and late (1-12 April) preincubation periods during 2002-2003. Females consumed 22 food types including low sagebrush (Artemisia arbuscula Nutt.), big sagebrush (Artemisia tridentata Nutt.), 15 forb species, 2 insect taxa, sagebrush galls, moss, and a trace amount of unidentified grasses. Low sagebrush was the most common food item, but forbs were found in 89% of the crops and composed 30.1% aggregate dry mass (ADM) of the diet. ADM and species composition of female diets were highly variable between collection periods and years, and coincided with temporal variation in forb availability. Adult females consumed more forbs and less low sagebrush compared to yearling females. Because of higher levels of crude protein, calcium, and phosphorus, forbs were important diet components in comparison with low sagebrush, which had the lowest nutrient content of all foods consumed. Our results indicate that increased forb abundance in areas used by female sage-grouse prior to nesting would increase their forb consumption and nutritional status for reproduction. We recommend that managers should emphasize delineation of habitats used by preincubating sage-grouse and evaluate the need for enhancing forb abundance and diversity.