Description Eurasian Eagle Owl (Bubo bubo) - The Eagle Owl is a large and powerful bird, slightly smaller than the Golden Eagle. It is the largest species of owl with a wingspan of up to 200 cm. Adult females can weigh in excess of 4 kg (9 lb), in comparison the common Barn Owl weighs about 500 grams (1.1 lb). It mainly feeds on small mammals, but can kill prey up to the size of foxes and young deer (up to 10 kg/22 lb), if taken by surprise. Larger prey (over 3 kg/7 lb) is consumed on the ground which leaves the bird vulnerable (for example to other foxes). It will also take on other birds including birds of prey.