[Illustration: GREAT NORTHERN DIVER. Chapter iv.] CHAPTER IV. DIVERS, GREBES, AND CORMORANTS. _Divers—Affinities and characteristics—Great Northern Diver—Black-throated Diver—Red-throated Diver—Grebes—Characteristics—Changes of Plumage—Great Crested Grebe—Red-necked Grebe—Black-necked Grebe—Sclavonian Grebe—Little Grebe—Cormorants—Characteristics—Changes of Plumage—Cormorant—Shag—Gannet._ The birds included in the present chapter belong to three well-defined families. None of them are so completely pelagic as the Auks, and yet, according to season, many of them are interesting features in the bird-life of the coast. Unfortunately for the summer visitor to the seaside, the Divers will be absent. They are birds that resort chiefly to inland districts to rear their young, or are only known as winter visitors to the British Coasts. The Divers form a small but well-marked family known as Colymbidæ, consisting of a single genus _Colymbus_, into which are grouped the four species that are now known to science. The Divers are allied to the Auks on the one hand, to the Grebes on the other, although systematists are not yet agreed upon the degree of their relationship. United, these three families form Dr. Sclater’s order Pygopodes. In every way the Divers are remarkably well fitted for an aquatic life. Their strong tarsi are laterally compressed, a form best suited for cleaving the water, the hind toe is well developed, and on the same plane as the rest, the feet are webbed, the bill is long, straight, spear-shaped and conical, admirably adapted for seizing the finny prey, the wings are comparatively short, yet capable of bearing the bird at great speed, the tail is short and fairly developed. The Divers in nuptial plumage are remarkably handsome birds, the neck being striped or richly marked, and the upper plumage beautifully spotted or adorned with white bars. They are all more or less gregarious birds during winter, and well marked social tendencies are displayed in some species during the breeding season. Their migrations, if comparatively short, are pronounced and regular. The young are hatched covered with down, able to swim with ease almost immediately. Adults moult in autumn, and assume their nuptial plumage in winter—a period doubtless when they pair—the winter plumage thus being carried for a short time. Young Divers carry their first plumage through the winter until the following spring (not moulting in December with their parents), when they assume their summer plumage, but the nuptial ornaments are not so brilliant in colour as in adults. Whether the vernal change in colour is effected without moulting, as in the Auks and some of the Limicolæ, appears not to have yet been ascertained. All the species of Divers are visitors to the British Islands, but only two breed in them, and one is an exceptionally irregular straggler. This is the largest of them all, the