From PinataIsland.info, the Viva Piñata wiki
Each piñata resident in your garden has a happiness rating, that reflects the quality of the care that you have been providing for it. If it stays very sad for a while, it will walk out of the garden and return to the wild.
A pinata's happiness is shown on the happiness meter and in the expression on the face within the happiness meter. You can see the happiness meter when you move your cursor over the piñata. Happier piñata are worth more chocolate coins. You can spot a very sad piñata from a distance -- it will be crying.
You can make a piñata happier by:
- Naming it.
- Directing it to eat a seed, flower, fruit, vegetable, or produce that it enjoys.
- Directing it to a pond.
- Watering it with the watering can (if it likes that sort of thing).
- Directing it to eat happy candy or joy candy.
- Buying it an accessory.
Some things that can make pinatas sad are:
- Getting squashed underfoot by other piñatas.
- Getting hit by the shovel.
- Seeing other piñatas get whacked by the shovel, broken, injured, poisoned, or eaten.
- Being in close proximity to another piñata that is higher up on the Food chain.
- Being in a garden that is no longer attractive to it (i.e. requirements no longer met).
Helpers also have a happiness rating that affects their behavior.