Final answer:
Birdseed is an effective reward for a bird learning to tap a lever because it is a primary reinforcer, satisfying the bird's fundamental need for food.
Step-by-step explanation:
When a bird learns to tap a lever and is reinforced with birdseed, the birdseed serves as an effective reward because it is a primary reinforcer. A primary reinforcer has innate reinforcing qualities that are not learned. This category includes fundamental needs such as food, water, and shelter, which do not decrease in value regardless of the environment.
A secondary reinforcer, on the other hand, includes things like money or praise, which only have reinforcing qualities if they can be used to obtain primary reinforcers or are associated with them. Thus, since birdseed satisfies a basic need - hunger - it is considered a primary reinforcer and is effective at encouraging the bird to repeat the behavior of tapping the lever.