Sexual size and beak differences likely evolved due to constraints imposed by the size differences, with male birds tending to be smaller than females, allowing conservation of energy to forage competitively and participate more frequently in courtship.
Sexual size and beak differences likely evolved due to constraints imposed by courtship because mating displays of male hummingbirds require complex aerial maneuvers and are costly in terms of energy. Males tend to be smaller than females, allowing conservation of energy to forage competitively and participate more frequently in courtship.