This bird is of the order of _natatores_, or swimmers; family,
_anatidae_, of the duck kind; genus, _anas_, or duck. The most striking
character of the swimming bird is derived from the structure of the
_feet_, which are always palmate--that is, furnished with webs between
the toes. There are always three toes directed forward, and these are
usually united by a membrane to their extremities; but, in some cases,
the membrane is deeply cleft, and the toes are occasionally quite free,
and furnished with a distinct web on each side. The fourth toe is
generally but little developed, and often entirely wanting; when
present, it is usually directed backward, and the membrane is sometimes
continued to it along the side of the feet. These webbed feet are the
principal agents by which the birds propel themselves through the water,
upon the surface of which most of them pass a great portion of their
time. The feet are generally placed very far back, a position which is
exceedingly favorable to their action in swimming, but which renders
their progression on the land somewhat awkward.
[Illustration: THE EIDER DUCK.]
The _body_ is generally stout and heavy, and covered with a very thick,
close, downy plumage, which the bird keeps constantly anointed with the
greasy secretions of the caudal gland, so that it is completely
water-proof. The _wings_ exhibit a great variety in their development;
in some species being merely rudimentary, destitute of quills, and
covered with a scaly skin--in others, being of vast size and power, and
the birds passing a great part of their lives in the air. The form of
the _bill_ is also very remarkable; in some, broad and flat; in others,
deep and compressed; and in others, long and slender.
Most of these birds live in societies, which are often exceedingly
numerous, inhabiting high northern and southern latitudes.
The distinguishing characteristic of the family of the _anatidae_ is the
_bill_, which is usually of a flattened form, covered with a soft skin,
and furnished at the edges with a series of _lamellae_, which serve to
sift or strain the mud in which they generally seek their food. The feet
are furnished with four toes, three of which are directed forward, and
united by a web; the fourth is directed backward, usually of small size,
and quite free. They are admirable swimmers, and live and move on the
water with the utmost security, ease, and grace. Such is their
adaptation to this element that the young, immediately after being
hatched, will run to it, and fearlessly launch themselves upon its
bosom, rowing themselves along with their webbed feet, without a single
lesson, and yet as dexterously as the most experienced boatman. They are
generally inhabitants of the fresh waters, and for the most part, prefer
ponds and shallow lakes, in which they can investigate the bottom with
their peculiar bills, without actually diving beneath the surface; yet
at some seasons they are found along the borders of the sea. Their food
generally consists of worms, mollusca, and aquatic insects, which they
separate from the mud by the agency of the lamellae at the margin of the
bill; but most of them also feed upon seeds, fruits, and other vegetable
substances.