The order of the Natatores, or Swimmers, comprises a number of Birds which are as much or even more at home in the water than upon the land. In accordance with their aquatic habit of life, the Natatores have a boat-shaped body, usually with a long neck. The legs are short, and placed behind the centre of gravity of the body, this position enabling them to act admirably as paddles, at the same time that it renders the gait upon dry land more or less awkward and shuffling. In all cases the toes are "webbed" or united by membrane to a greater or less extent (fig. 332, A).
Fig. 332. - Natatores. A, Foot of Cormorant (Phalacrocorax); B, Beak of the Bean-goose (Anser segetum).
In many instances the membrane or web is stretched completely from toe to toe, but in others the web is divided or split up between the toes, so that the toes are fringed with membranous borders, but the feet are only imperfectly webbed. As their aquatic mode of life exposes them to great reductions of temperature, the body of the Natatorial birds is closely covered with feathers, and with a thick coating of down next the skin. They are, further, prevented from becoming wet in the water by the great development of the coccygeal oil-gland, by means of which the lustrous plumage is kept constantly lubricated and waterproof. They are usually polygamous, each male consorting with several females; and the young are hatched in a condition not requiring any special assistance from the parents, being able to swim and procure food for themselves from the moment they are liberated from the egg. The Natatores are divided into the following four families: -Fam. 1. Brevipennatae. - In this family of the Swimming birds the wings are always short, and are sometimes useless as organs of flight, the tail is very short, and the legs are placed very far back, so as to render terrestrial progression very difficult or awkward. The family includes the Penguins, Auks, Guillemots, Divers, and Grebes. In the Penguins (Spheniscidae) the wings are completely rudimentary, without quills, and covered with a scaly skin. They are useless as far as flight is concerned, but they are employed by the bird as fins, enabling it to swim under water with great facility, and they are also used on the land as fore-legs. The feet are webbed, and the hinder toe is rudimentary or wanting. The Penguins live gregariously in the seas of the southern hemisphere, on the coasts of South Africa and South America, especially at Tierra del Fuego, and in the solitary islands of the South Pacific. When on land the Penguins stand bolt upright, and as they usually stand on the shore in long lines they are said to present a most singular appearance. The best-known species are the Jackass Penguin (Spheniscus demersus) of the Falkland Islands, and the King Penguin (Aptenodytes Patagonica) of the Straits of Magalhaens. Some Penguins have the extraordinary habit of forming no nest, but of carrying their egg about with them in a temporary pouch of the abdominal integument. In the Auks (Alcidae) the wings are better developed than in the Penguins, and they contain true quill-feathers; but they are still short as compared with the size of the body, and are of more use as fins than for flight. The Great Auk or Gare-fowl (Aka impennis) is remarkable for being one of the birds which appear to have become entirely extinct within the human period, having been, in fact, destroyed by man himself. It abounded at one time on both the American and European sides of the North Atlantic, and used to visit the shores of Scotland in summer for the purpose of breeding. The Little Auk (Mergulus alle) occurs still in abundance in the seas of northern regions. Other well-known members of this group are the Razor-bill, the Puffins (Fratercula arctica), and the Guillemots (Uria). The Guillemots have a short tail, narrow and pointed wings, short feet, and no hallux. Like the other members of the family they inhabit northern and polar regions.
Fig. 333. - Jackass Penguin (Spheniscus demersus).
In the Divers (Colymbidae), comprising the true Divers and the Grebes, the power of flight is pretty well developed, but the bird still is much more active in the water, swimming or diving, than on land. The Grebes are not uncommon in Britain, and are largely killed for making muffs, collars, and other articles of winter dress. They have the membrane between the toes deeply incised. They haunt the sea as well as lakes and rivers, and swim and dive admirably. In the Divers proper the front toes are completely united by a membrane. The Northern Diver or Loon (Colymbus glacialis) is a familiar example, and is found on the coasts of high northern latitudes.
Fam. 2. Longipennatae. - This family of Natatores is characterised by the well-developed wings, the pointed, sometimes knife-like, sometimes hooked bill, and by never having the hallux united with the anterior toes by a membrane. The following are the more important groups coming under this head:
a. Laridae, or Gulls and Terns, having powerful wings, a free hinder toe, and the three anterior toes united by a membrane. The Gulls form an exceedingly large and widely distributed group of birds; and the Terns or Sea-swallows are equally beautiful, if not quite so common. The Terns are distinguished by their long and pointed wings, forked tail, and comparatively short legs. They fly with great rapidity over the surface of the sea, from which they pick up their food.
b. Procellaridae, or Petrels, closely resembling the true Gulls, but having a rudimentary hinder toe, and having the upper mandible strongly hooked. The smaller species of Petrel are well known to all sailors under the name of Storm-birds and Mother Carey's Chickens. They are nocturnal or crepuscular in their habits, breed in holes in the rocks, lay but one egg, and are almost all of small size and more or less sombre plumage. The largest member of the group is the gigantic Albatross (Diomedea exulans), not uncommonly found far from land in both the northern and southern oceans. The Albatross sometimes measures as much as fifteen feet from the tip of one wing to that of the other, and the flight is powerful in proportion.