We examined 11 Eagle Owl Bubo bubo nests in Mongolia during 2004–06. Five nests were located in cliffs, three in rock columns, two in sandy precipices and one on a rock ledge. Mean height (above ground) of the nest site structure was 7.6 (SD 5.9) m and height of nest entrance was 3.1 (SD 2.5) m. Mean clutch size was 1.7 (SD 0.9) and the number of fledglings was 1.5 (SD 0.5). Nest structure or entrance height did not correlate with the number of eggs laid (r = 0.1, r = 0.4) or young fledged (r = 0.001, r = 0.1). We identified 276 prey from pellets and remains from nests or nearby perches. Pellets averaged 63.5 (SD 14.2) by 22.2 (SD 4.1) mm and weighed 10.6 (SD 4.6) g when collected. Seventeen species of birds were taken as prey, and represented 32.2% of prey biomass (26.1% by frequency), while 13 mammal species constituted 67.8% of the biomass (72.2% by frequency). The most frequent avian prey was the Eurasian Sparrowhawk Accipiter nisus; the most frequent mammalian prey was the Mongolian Five-toed Jerboa Allactaga sibirica. Amphibians and beetles together represented a very small percentage (0.23%) of the diet biomass.
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Vol. 97 • No. 4