Why can ducks and other waterfowl stay in cold water for a long time and not get overcooled?

The duck’s chest and abdomen, that is, parts of the body that are immersed in water, are covered with thick down in the duck, which is tightly covered from above with feathers that protect the down from water. Thanks to the down cover, the body of the duck is surrounded by a layer of warm air and does not come into direct contact with cold water. The subcutaneous layer of fat, which is more developed in waterfowl than in land birds, also helps to maintain heat.