(noun) A bird that has distinctly different plumage than the standard colors for its species. This classification applies only to adult birds, as subadult birds frequently have different plumages but as they mature they will have the characteristic adult markings. A morph bird will maintain its color differences throughout different seasonal molts.
Many bird species feature different plumage morphs, though they are most well documented among birds of prey. Red-tailed hawks, in particular, have several different plumage morph variations. Other birds may have just a few morphs, including standard, light and dark birds, and many of these variations occur geographically with birds in different regions exhibiting slightly different plumages. Songbird morphs, such as the green pine siskin, are very rare.
Morphs are distinctly different from dimorphic birds. A dimorphic bird has different plumages between genders, while the term morph refers to color variations that can affect either sex.