sexual dimorphism in hummingbirds
...that of 15 degrees of the males. Such sexual dimorphism evolved through the ecology of feeding; the difference in bills enables both sexes to eat different foods. The only food plants available to the caribs are red-bracted H. caribaeas and green-bracted H. bihais. Both sexes differ in the way they use the two species. The males are more settled and tended to control and defend the densest stands of H. caribaea, which bears three times as many flowers as H.bihai. Females behaved differently. Because females have to incubate eggs and raise offspring without male assistance, they can’t guard flower patches and therefore must feed from undefended patches. The females’ smaller size prevents them from competing successfully against males for the richest territories (H. caribaeas). Now that we know what plants each sex feeds on, the differences in flowers of the two species of plant will explain why the bills of the sexes are different. The H.caribaea flower, dominated by male pollinators, is shorter and straighter than the flowers of H. bihai. They are shorter than the H. bihai flower by six millimeters, which is also how much the males’ bill differs from the females’. The H. caribaea flowers are curved at a 20 degrees arc, which suits the males’ bill, whereas the curvature of the H.bihai flowers matched the females’ bills by curving 30 degre...