Katzner analyzed eagle pellets to find out what the birds were eating. Birds of prey eat animals whole. The regurgitated material consists of hard oval pellets, each about two to four inches in length. During his summers in Kazakstan, Katzner analyzed more than 3,000 eagle pellets. He collected the pellets near nests or under large roosting trees.
Eagles eat almost any kind of small animal.
Katzner's subjects appear to have narrowed their choices. Steppe eagles eat voles, lots of mice, and small ground squirrels. The imperial eagles eat ground squirrels and marmots. However, Katzner also observed diet variations within each species. Imperial eagles nesting close to colonies of rooks will eat lots of rooks.