Down Feather - Description and Etymology

Description and Etymology

The word down comes from the Old Norse word dūnn, which had the same meaning as its modern equivalent. The down feather is considered to be the "simplest" of all feather types. It has a short or vestigial rachis (shaft), few barbs, and barbules that lack hooks. There are three types of down: natal down, body down and powder down. Natal down is the layer of down feathers that cover most birds at some point in their early development. Precocial nestlings are already covered with a layer of down when they hatch, while altricial nestlings develop their down layer within days or weeks of hatching. Megapode hatchlings are the sole exception; they are already covered with contour feathers when they hatch. Body down is a layer of small, fluffy feathers that lie underneath the outer contour feathers on a bird's body.

Powder down is a special type of down that occurs in a few groups of apparently unrelated birds. In some species, the tips of the barbules on powder down feathers disintegrate, forming fine particles of keratin, which appear as a powder, or "feather dust", among the feathers. These feathers grow continuously and are not molted. In other species, powder grains come from cells that surround the barbules of growing feathers. These specialized feathers are typically scattered among ordinary down feathers, though in some species, they occur in clusters. All parrots have powder down, with some species (including the Mealy Parrot) producing copious amounts. It is also found in tinamous and herons. The dust produced from powder down feathers is a known allergen in humans.