EIDER-DOWN BLANKETS An eider-down has come to mean a comforter, a sleeping bag, or even a padded jacket. But to an ornithologist eider down still has its older meaning: the down of an eider duck. It is this material gathered from the eider ducks' nests which forms the article of commerce. The eider's nest may contain grass, seaweed, and sticks, but it is notable for the blanket of down on which the eggs rest, and with which the female covers the eggs when she leaves them. This down is plucked from the breast of the female. If it is taken from the nest she replaces it with more, and it is on this principle that harvesting of the down is carried out. On islands and islets in the northern part of the North Atlantic eiders nest in great numbers in dense colonies. Some of these are jealously guarded by the local inhabitants, who gather the first blanket of down from the eggs, and later, after the eggs have hatched, gather the second crop of down with which the female has replaced the first to guard her eggs against the inclement weather of those boreal latitudes. Each nest may yield an ounce or so of the precious down, which is carefully cleaned and sent to market. It is this material, extremely light, extremely elastic, and one of the best non-conductors of heat, which finally becomes the important part of real eider-down comforters, sleeping bags, and padded jackets. SYMBIOSIS--ANIMALS LIVING IN MIXED HOUSEHOLDS [Illustration] Symbiosis, a term from the Greek, is what the biologist uses for the living together of two dissimilar organisms. In a broad sense it includes such diverse relations as the lice living on man and rats in his house, the union of an alga and a fungus to form a lichen, and the cross-pollination of flowers by hummingbirds. The story of the burrowing owls of our Western plains living in amity with prairie dogs and rattlesnakes as one happy family comes to mind as an example. But "foolish nonsense" is how the noted biographer of North American birds, A. C. Bent, characterizes such stories. He then goes on to quote evidence as to what actually happens, and one can see how the story originated. The prairie dogs, which are really plump, dumpy, ground squirrels and not dogs at all, dig their burrows close to each other on the prairie in colonies which have come to be called prairie-dog towns, or dog towns or simply "towns." Burrowing owls also take up their residence in these towns, probably because they find burrows ready made and do not have to dig their own as they are quite able to do.