Callum's egg was one of many dormant Blue Owl eggs flown to the Northern Kingdoms to be hatched. His egg was mainly brooded by a blue Pygmy Owl named Shui, who became attached to the egg. When the hatchery was attacked by wolves, Shui managed to grab the egg and hide in a small cavern until the wolves had left. Shui, lost, flew through the Northern Kingdoms with the egg, flying in the direction she felt the Middle Kingdoms were. She eventually settled in The Beaks, unaware of its danger, and likened it's ideal conditions to the luxury of the crystal palace. Absorbed with herself, Shui forgot about the egg, which hatched on the lunar eclipse.
Callum matured quickly, living in a cave near the border of The Beaks, an area that was more heavily forested. There was a Barred Owl family that lived nearby, and Callum would listen as the father told his owlets the legends of Ga'Hoole. Callum, liking the sound of the father's name, chose it as his own.
Despite not being fully aware of what kind of bird he was, Callum felt that he must hide from the outside world. He liked what he heard about Ga'Hoole, and thought how he might be accepted there.