Animals follow a realistic model in the jungle. They evolve from a new born to juvenile and adult version, sometimes even to an elder one.

The indicators for their growth state is the animals level and the amount of mana.
All animals gain 50 points of mana per day and evolve to their next level until they reach maturity (level 3 for most animals). Mature animals LOSE 50 mana per day, animals that have lost all mana die of old age and are removed from the map.
There is a slim chance of animals becoming elder versions of their race when they reach the end of their existance.