The best showoff wins and he is usually the dominant male who maintain a position in the center of the arena. He will mate with several females. He offers only genes, that is all he needs to offer because the female does not really need him after the clutch is complete. She incubates and the young are precocial . In most cases most of the incubation is done by the female.
Most species build a nest, but some birds build no nest, e.g., killdeer.
It is well known that some birds migrate long distances. Zoologists are most interested in what triggers migration , physiological changes that occur before migration, and the mechanisms of navigation . The urge to migrate is instinctive not learned. Photoperiod affect gonad development. It also affects fat deposition.