(noun) A patch of often iridescent color on the secondary feathers of most duck species. The color of the speculum will vary by species, as will its width and any non-iridescent borders. The mallard, for example, has a blue-purple speculum with distinct black and white bordering. The speculum is typically brighter in males, just as most drakes have flashier overall plumage. In addition to ducks, some parrot species and other birds also have a distinct speculum, though less often iridescent. Depending on how the bird holds its wings, the speculum may not be visible when perched or at rest, but it is always visible in flight.
To use the speculum for bird identification, watch the color carefully in bright sunlight to gauge its true shade, and note any borders. Also note the length and width of the speculum compared to the bird's overall wing size, and note how much of it, if any, is visible when the bird is at rest.
Photo – Mallard Speculum © Peter Trimming
SPEH-cue-lumm
