Answer:
The researcher used the comparative method to explore the courtship behavior variation between closely related species.
Explanation:
Comparative research method:
It is a research technique which is used to compare the features, cultures, or anything from similar to different behavior.
This is the best example of comparative research method because she compared the courtship behavior in species which are closely related. After comparison, she found that ancestral form is simple courtship dances while derived form is complex courtship dances.
So, according to this example the research approach used is the comparative research method.