Contra Free Loading Research has shown (with 100s of species and 100s of repetitions) that given the choice of free food or contingent food the animals will choose contingent food. In other words, they choose to work for food than get it for free.
The rationale behind this; by working for the food they have control over it. This is about animals operating in the environment (operant conditioning).
When animals are allowed to exercise this type of choice making it has been scientifically proven that they become bolder and more confident.