Thus, eastern imperial eagles appear to prefer rodents and similar small mammals that are burrow-dwelling and/or partial to ground dwelling in open grass or fields along wooded edges. Assorted bird species may factor heavily into the diet of eastern imperial eagles. More than 120 bird species are known to be taken by this eagle. European studies reflect the high importance of common pheasants ("Phasianus colchicus"), in Europe a non-native gamebird (although the imperial eagle also encounters and hunts the species extensively in its native range as well), in their foods. In the aforementioned large Hungarian study, pheasants were the third most frequently taken prey species, making up 12% of the diet. In the Czech Republic, the pheasant ranked third as well. In Slovakia, the pheasant was second only to the hare in frequency, comprising 17.3% of the foods, although exclusively juvenile and hen pheasants (no cocks) were reportedly taken. In Bulgarian studies, the domestic chicken ("Gallus gallus domesticus") seems to take the place of pheasants in their diet, making up 10.8% and 20.8% at Saker mountain and Dervent heights and second most frequently taken prey at both, respectively. The largest study of the eastern imperial eagle’s dietary habits known occurred in the vast Naurzum Nature Reserve in Kazakhstan, where 11,079 prey items were reviewed. The prey spectrum was exceptionally diverse here, with no one prey reliably being favored by the imperial eagle pairs, despite an ample colony of yellow ground squirrel ("Spermophilus fulvus") and russet ground squirrel ("Spermophilus major") being nearby and at least three other species of eagles with nearby nesting sites presenting possible resource competition. Without presenting the metrics, apparently birds were the highest volume prey for the imperial eagles, especially corvids, namely the rook ("Corvus frugilegus") and Eurasian magpie ("Pica pica"), numerous species of duck as well as Eurasian kestrels ("Falco tinnunculus") and little bustards ("Tetrax tetrax"). In East Thrace, Turkey, the second most regularly taken prey species is the yellow-legged gull ("Larus michahellis"), which comprised more than 12% of the diet by number and 13.8% of the prey biomass. Additionally in East Thrace, a high volume of white storks ("Ciconia ciconia") was taken, making up 11.3% of the biomass.