The Eurasian Eagle-Owl is a very large, powerful bird, smaller than the Golden Eagle but larger than the Snowy Owl. It's often called the world's largest owl, tho the Blakiston's Fish Owl is slightly heavier and the Great Grey Owl is slightly longer.
They're still babies. Look at the body language: Altia, a 7 week old Siberian Eagle Owl, the largest species of owl in the world meets Powys, a 5 week old Little Owl. The pair are being raised at The Scottish Owl Centre in Scotland’s central belt.