Down
A type of feather where the shaft (RACHIS) is more or less absent and each barb is long and fluffy. In adult birds down forms a kind of underwear beneath the main feathers, while chicks develop a covering of down ('natal down' or 'neossoptile' feathers) varying in thickness according to species. Down feathers may also be called 'plumules'. Their main function is insulation.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver