(adjective) Having glossy, rainbow-like colors that change color when seen from different angles or in different light conditions. Iridescent colors often have a shimmering or metallic quality, often described as similar to an oil sheen. In birds, iridescent coloration is most commonly caused by a prismatic feather structure that scatters and refracts light at the microscopic level to give the feathers their changing colors.
Many birds have iridescent feathers or an iridescent sheen on their overall plumage. Examples include the colorful throat patch of many male hummingbirds, the wing speculum patch on many ducks, the sparkling neck patch of the rock pigeon, the rainbow pattern on the wings of the common bronzewing or the subtle green or purple sheen on the heads of greater scaups and lesser scaups. Birds with an overall iridescent gloss to their plumage include the European starling, common grackle and shiny cowbird.
When using iridescent plumage to help identify a bird, it is best to observe the bird's plumage in moderate to bright sunlight that will best highlight the color. Watch as the bird moves to see how the color changes, and note the overall base color of the iridescence – in many cases, one dominant color will show in the iridescence, such as blue, purple or green. Also note the extent of the iridescence and how far over the bird's body it extends, as well as how many different colors are part of the iridescence.
Photo – Ruby-Throated Hummingbird © jeffreyw
Iridescence (noun), Pearlescent