<\/a>Courtesy Photo \/ Mark Schwan \n Gray plumage of this raven indicates a failure of melanin synthesis, probably early in development.<\/p><\/div>\n\t\t\t\t
Observations of captive birds have shown the importance of carotenoids in the diet. For instance, male house finches on a diet of seeds (which are low in carotenoid content) don’t develop the characteristic red on head and chest—those feathers become pale yellow. But if fed supplemental carotenoids, the pale males grow nice red feathers the next time they molt. Similar changes have been noted in a number of other species in captivity, including flamingos, spoonbills, scarlet ibises, tanagers, and woodpeckers. In some cases, the supply of carotenoids also determines the color of the bill (e.g., zebra finches) or the color of facial skin (e.g., snowy egrets).<\/p>\n\t\t\t\t
A major dietary source of carotenoids for many terrestrial birds comes indirectly from the leaves of plants: Birds that eat foliage-eating insects get yellow carotenoids (such as lutein) from their prey. For instance, European great tits have yellow breast feathers that are colored by carotenoids in the herbivorous caterpillars that they often eat. It turned out that tree leaves in urban environments (in Sweden) have less lutein than those in rural areas, so urban great tits are not as yellow as rural ones.<\/p>\n\t\t\t\t
Egyptian vultures have yellow facial skin colored by carotenoids. The vultures forage on carrion, including dead sheep, eating not only the meat but also the feces in the guts. Sheep in green pastures have more carotenoids in their food and feces than sheep in dry, brown pastures, so vultures in the green pastures have yellower faces than the others.<\/p>\n\t\t\t\t
Flamingos, spoonbills, and some other wading birds obtain red carotenoids by eating small aquatic crustaceans that contain these pigments, derived from planktonic algae. In addition, they can chemically convert yellow carotenoids from phytoplankton to red to achieve their colorful feathers.<\/p>\n\t\t\t\t
Birders in eastern North America were astonished, decades ago, to observe that cedar waxwings were looking odd.<\/p>\n\t\t\t\t