Answer: Observational study is correct.
Explanation:
It is a type of observational study.
Observational study is a study in which individuals are observed and outcomes are measured depends upon individuals.
As we have given that a biologist sets up cameras to record all the animals that come to a watering hole over a 30 day period.
So,
In the above situation , a biologist is observing all the animals for 30 days, and then he will measure the certain outcomes.
Hence, observational study is correct answer.