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 {52}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. [Illustration: FIG. 16.–Little Grebe. _Podicipes fluviatilis._ × ¼.]