Collect the indicated number of medals in three of the five contests one of the following locations. After winning two of a certain type of medal in that location, the corresponding cub will hide somewhere in the area. After earning a third medal of the same type, your current cub will find the hidden cub and a cinematic will play, unlocking the cub.

Bobcat: Win three silver medals at Cherry Blossom Grove.
Borneon Clouded Leopard: Win three bronze medals at Woodland Glade.
Saber-tooth Tiger: Complete the game and earn a medal in the last contest of Celestial Glacier.
Serval: Win three bronze medals at Fiddler's Beach.
Siberian Tiger: Win three gold medals at Suri Mountain.
White Jaguar: Win three silver medals at La Selva.