During summer pikas do not store fat for the winter months; hay piles are the main energy source in winter. All the hay piles collected in an area where pikas (Ochotona princeps) coexisted with marmots (Marmota flaviventris) contained marmot scats. Marmot scats had a higher energy density than the most abundant type of vegetation in hay piles.
In feeding trials pikas on a diet of hay pile vegetation plus marmot scats consumed significantly less food per day than they did on a diet of hay pile vegetation alone. These findings suggest that pikas coexisting with marmots use marmot scats to supplement the energy contained in the vegetational component of hay piles.
Gessaman, James A. and Goliszek, Andrew G.
"Marmot scats supplement hay pile vegetation as food energy for pikas,"
Great Basin Naturalist: Vol. 49
, Article 18.
Available at: http://scholarsarchive.byu.edu/gbn/vol49/iss3/18