Daniel is a hunter, and he is out in a duck blind watching for ducks flying overhead. based on what is known about schedules of reinforcement, you should conclude that daniel's watching behavior is likely to be reinforced based on a:

Based on a "variable-interval schedule".

A variable interval schedule refers to a sort of operant conditioning reinforcement schedule in the process support is given to a reaction after particular measure of time has passed, the amount of time which is not predictable, yet this measure of time is on a changing/variable schedule.