Costs and Benefits of Subadult Plumage in Mute Swans: Testing Hypotheses for the Evolution of Delayed Plumage Maturation.

In some avian species, young birds capable of reproducing diminish their prospects of doing so by molting into a subadult plumage that accurately signals their subadult status. Several hypotheses have been proposed to explain the evolution of delayed plumage maturation, but testing them usually has involved interspecific comparisons that are hard to interpret. Mute swans (Cygnus olor) exhibit two phenotypes that differ in whether the birds have a gray subadult plumage (SAP phenotype) or molt immediately into an all white adult plumage (AP phenotype).