Context: In polygynous species with considerable sexual dimorphism, males tend to return earlier to the breeding sites than their females. This is termed protandry.

Question: What is it called when males return earlier to the breeding sites than females?
Answer: protandry

Question: What happens in polygynous species with sexual dimophism?
Answer: males tend to return earlier to the breeding sites

Question: Why do males in polygynous species return before the females?
Answer: sexual dimorphism