At the credits screen, if you tap the lion at the bottom of the screen, it will put a piece of trash in the trash can. Tap the lion again to make it take the piece of trash out.

To unlock all animals, foliage, buildings, and other objects, at the main menu, press UP(2), DOWN(2), LEFT, RIGHT, LEFT, RIGHT, UP(2), DOWN(2), LEFT, RIGHT, LEFT, RIGHT.

Activate the following cheats by changing the guest's names to the corresponding names:

CHEAT FUNCTION - NAME
All animal houses - "Andrew Binder"
All animal shelters - "John Wheeler" or "Adam Levesque"
All animal toys - "Lou Catanzaro"
All foliage - "Charlie Peterson"
All scenarios completed - "Akiyama"
Money is donated to zoo - "Bill Gates"
Animals breed more frequently - "Dr Dolittle"
Endangered animals -"Steve Serafino"
Sick guests - "Zeta Psi"
Blue shirts - "Mr. Blue"
Brown shirts - "Mr. Brown"
Orange shirts - "Mr. Orange"
Pink shirts - "Mr. Pink"
White shirts - "Mr. White"
Yellow shirts - "Mr. Blonde"

Four bonus scenarios can be unlocked by completing a scenario on different difficulty settings.