It's a pocket of skin that acts like a second womb, giving the joey a safe, cozy environment to grow. And, like a pregnant belly, the pouch can stretch to fit the baby as it gets bigger.

Visitors can see the joey and its mother in the Bronx Zoo’s JungleWorld exhibit. It is believed there are only about 2,500 Matschie’s tree kangaroos left in the wild, in their native Papua New ...