A Mama for Owen by Marian Dane Bauer, illustrated by John Butler

From chapters.ca:
Owen the baby hippo and his mama were best friends. They loved to play hide- and- seek on the banks of the Sabaki River in Africa. That was all before the tsunami came and washed Owen's world away. But after the rain stops, Owen befriends Mzee, a grayish brown tortoise. He plays with him, snuggles with him, and decides he just might turn out to be his best friend and a brand- new mama. Inspired by the tsunami of 2004, acclaimed storyteller Marion Dane Bauer and celebrated illustrator John Butler depict this heartwarming true tale of healing, adoption, and rebirth - with splendid illustrations and oodles of love.