Animals alter resource use as conditions change and these changes could have significant consequences on demography. We generated a logistic resource selection probability function for habitat use and estimated percent composition of diets by pronghorn (Antilocapra americana) in Yellowstone National Park during winter to assess if selection of sagebrush (Artemisia) has changed since the 1960s, corresponding with diminishing sagebrush and increasing seral species such as rabbitbrush (Chrysothamnus). We located 37 radiocollared adult females in 1,440 different groups during December 1999 through March 2005 and compared habitat attributes to 9,347 randomly selected points from the winter range. Pronghorn preferred greasewood (Sarcobatus vermiculatus) and selected grasslands in comparison to the sagebrush cover type. The relative selection against sagebrush may stem from a substantial decrease in this plant type on the winter range by the 1960s due to intense browsing by congregated ungulates. The percent composition of sagebrush in the winter diets of pronghorn decreased from 67% during 1985–1988 to <10% during 2000–2001, while rabbitbrush increased from 5% to 60%. These findings and the results of companion time-series analyses suggest the winter range for Yellowstone pronghorn may not support larger populations (>500) of pronghorn for sustained periods, as occurred historically. Similar effects from habitat fragmentation and degradation face managers of migratory ungulates worldwide.