A rare tree kangaroo born in The Bronx at the end of December ... At birth, the tree kangaroo joey is the size of a jellybean, and the majority of its physical development occurs in the mother ...

However, the kangaroos are not fully formed when they are born. Newborn joeys ... The teat will expand in the joey’s throat to keep them in place until they can suckle on their own at around two ...

The kangaroo joey in this video is a natural at hopping, quickly jumping on his own seconds after leaving his mom's pouch Kelli Bender is the Pets Editor at PEOPLE. She has been working at PEOPLE ...