Fig. 14.–Head of Ichthyornis. (From Geikie, after Marsh.) × ½.
Order I. ICHTHYORNITHES.
Enough has already been said with regard to the position of the Order Ichthyornithes, with its sole Family Ichthyornithidae; but it remains to discuss the several members. Ichthyornis victor, I. dispar, and the other species were small forms of about the size of a Partridge, with the habits and appearance, it is presumed, of Terns or Gulls.[[48]] The head was extremely large in proportion to the remainder of the skeleton; the beak was long and pointed, with entirely separate rami to the mandible; the sharp teeth, fixed regularly in distinct sockets, were inclined backwards, and occupied the whole of the lower and at least the posterior half of the upper jaw; the keel of the sternum was large and broad; the dorsal and cervico-dorsal vertebrae were biconcave, as in Archaeopteryx, and perhaps to some extent in Enaliornis; the quadrate articulated to the skull by one knob, as in the Neornithes Ratitae and Neornithes Odontolcae; the metatarsus was short and the whole foot small; a furcula was probably present; the wings were well developed, indicating great powers of flight; while the tail was comparatively short, and ended in a pygostyle. It will be observed that of these characters the formation of the jaw and its teeth, the biconcave vertebrae, and the articulation of the quadrate, are those that chiefly distinguish the Order from the rest of the Carinatae. Apatornis celer, also from the Cretaceous deposits of Kansas, is probably to be placed here, but other genera described from the same strata cannot yet be certainly classified.[[49]]
Order II. COLYMBIFORMES.
The Colymbiformes constitute a very archaic Order of Birds, and hold a somewhat isolated position. Older writers combined them with the Alcidae as a group Pygopodes, but recent anatomical investigations make it clear that Auks have more affinity to Gulls, which again trend to the Limicoline alliance. As regards structure, the two Sub-Orders Colymbi and Podicipedes, with their Families Colymbidae, or Divers, and Podicipedidae, or Grebes, may be here treated together. They are all water-birds with webbed or lobed toes and extraordinarily flattened metatarsi. The sternum in the Colymbidae is much longer than broad, in the Podicipedidae short and wide, while the furcula is Y-shaped; the neck is more or less elongated; the bill in the former Family is strong, straight, acute, and compressed, in the latter moderate and sometimes recurved, being either slender, as in Aechmophorus, or very stout, as in Podilymbus. The scutellated metatarsi are set very far back, and are fairly long, the procnemial process of the tibia being remarkably elongated, though Grebes alone have a distinct patella; the hallux is very small and has a small membrane, but whereas Divers have the anterior toes fully webbed, their allies have them surrounded by large lobes of skin, connected only at the base. The claws are abnormally broad and flat in Grebes, the outer margin of the third being serrated. In the Colymbidae the wing is short, narrow, and pointed, with eleven primaries and about twenty secondaries; in the Podicipedidae it is still shorter and concave in form, with twelve primaries but rarely twenty secondaries; in the latter no true rectrices can be distinguished, though a tuft of downy feathers exists, while in the former they are normal though much reduced, and number from eighteen to twenty. Grebes have bare lores, and are frequently adorned in the breeding season with crests or tippets of a golden or brownish colour; the dense glossy plumage being more commonly used for decorative purposes than the duller coats of Divers. The tongue is always long and pointed, the syrinx is tracheo-bronchial, the nostrils are pervious, an aftershaft is present, and both adults and young are uniformly downy. Fossil remains from the Oligocene of France and southern England, indicating a genus intermediate between the two Families, have been named Colymboïdes.[[50]]
Fam. I. Colymbidae.–Colymbus septentrionalis, the Red-throated Diver of the Arctic and sub-Arctic parts of both worlds, is brownish black in summer, with white under-parts and white specks above; the head and neck are lead-coloured, except the nape, which is black with white streaks, and the mid-throat, which is reddish-chestnut. C. arcticus, the Black-throated Diver, found in the same regions though with a different distribution, as for instance in Scotland, is blacker, with white bars as well as spots; the crown and hind neck being ashy grey, the sides of the latter striped with black and white, and the throat purplish-black, interrupted by a semi-collar of white with vertical black lines. C. pacificus of western North America is barely separable. C. glacialis, the Great Northern Diver, has a much more restricted range, breeding in Iceland, Greenland, and the Fur Countries as far west as the Great Slave Lake, where it meets C. adamsi (hardly differing except in the yellowish-white bill), which extends thence to Northern Asia, and possibly to Spitsbergen and Jan Mayen. The former is black above, with belts of white spots making a "chess-board" pattern; the lower surface is white, and the throat is crossed by two bands of white with longitudinal black bars, while the head and neck are black with a purplish gloss, changing to green below. In winter most Divers are found down to the northern tropic, at which season the throat becomes white, as it is in the young, in which the feathers of the upper parts are duller with whitish edges. The sexes are similar; the bill is normally black, and the feet are bluish or greenish grey. The downy chicks are sooty above.
Fig. 15.–Great Northern Diver. Colymbus glacialis. × ⅛.
Divers are not usually gregarious, and unless driven by stormy weather to inland waters, are essentially marine, except during the breeding season, when they ascend the rivers and seek their customary nesting-sites on the moors, the Black-throated species showing a somewhat greater preference than the rest for islands in the lakes they frequent, but the Red-throated often selecting small pools, or even "flows," among the heather. The two eggs, greenish- or reddish-brown in hue, with blackish and grey blotches and spots, are laid on a mere depression in the grass or sand close to the water's edge, or upon a mass of green vegetation which is occasionally semi-natant. Incubation is said to last four weeks. As a rule the female performs this duty, lying flat upon her eggs, and gliding or scrambling off when disturbed, whence a distinct track is often visible upon the turf. On leaving the land a dive is taken to a considerable distance, then both parents swim towards the intruder with the body partly submerged, and finally, if thoroughly scared, they rise heavily on the wing to circle round with outstretched neck before betaking themselves with rapid but laboured flight to some neighbouring lake, from which they return at intervals until the coast is clear. They descend from aloft noisily and with great impetus, the splashing plunge being followed by a gliding movement, leaving a broad furrow behind, while on land they move with difficulty, and rest on the metatarsus. Their croak, or loud, clear, melancholy cry is often heard before storms, whence the Red-throated Diver is called Rain-goose in Scotland; the food consists chiefly of fish, brought to the surface and swallowed with a jerk, but crustaceans, molluscs, and perhaps aquatic insects vary the diet. The young take to the water readily, but the female occasionally carries them on her back.
Both Divers and Grebes swim strongly, the flat of the metatarsus meeting the water during the back stroke, and the thin edge on the return. When submerged they do not use the pinions.