Fig. 107.—The Black Scissors-bill (Rynchops nigra).
The Scissors-bills have received their name from the conformation of their beaks, which are flattened laterally into two laminæ fitting one on the other, forming two mandibles compressed into cutting blades, the upper being one-third shorter than the lower. In order to pick up the shrimps and small fishes on which they feed, these birds are obliged to skim the surface of the water, dipping the lower mandible of their bill, the upper mandible being kept open and clear of the water till aquatic insects or other small fry have entered into the lower portion of it.[25] The singular form of their bills is also of service to them in opening such bivalve shell-fish as come in their way. They frequently watch these mollusks, and when they notice that the shell of the latter is slightly open, they plunge the lower mandible of their long bill into it; they then break the ligament of the shell by beating it against the rock. The tenement being thus destroyed, there is no obstacle to their devouring the inhabitant.
The only remarkable species of this bird is the Black Scissors-bill (Rynchops nigra), frequently called the Cut-water. It is about the size of a Pigeon; its prevailing colour is white, top of the head and shoulders black, with a white band on the wings. These birds are very numerous in the West Indian seas. They fly with a slow motion, and, like the Gulls and other sea-birds, they occasionally form such dense flocks that the sky is actually darkened for the space of a league.
Gulls and Allied Species.
Gulls and their congeners include the well-known shore-birds generally called Gulls, more especially the Skuas (Lestris), Gulls (Larus), and Mews (Gavia). They are characterised by a light body, more or less compact; neck of moderate length; head ovate; bill shorter than the head, straight, compressed; convex ridge on upper mandible, nasal groove long; lower mandible with the angle long and narrow; mouth moderate; tongue fleshy; eyes small; legs generally short; tibia bare; tarsus short, compressed; hind toe small; middle toe longest; fore toe moderate in length and slender; connecting membrane full, margins only concave; claws generally small, arcuate, acute, and more or less compressed.
These birds inhabit the sea-shore, along which they wander in search of food; the larger species preying on fish, crustacea and mollusca, and the carcasses of cetacea and other marine mammalia cast up by the sea. They all pursue shoals of fish in the open sea, often to great distances from land. Their plumage is full, soft, close, elastic, and well blended on the back and wings; wings long, broad, and pointed; the tail, of twelve feathers, rounded and forked.
The Sea Mews (Gavia) are connected with the Terns, yet still have some characteristics of the Gulls. However, they are of smaller size than the latter, have more slender forms, and their feet and bills are comparatively feebler. We shall describe the Mews and Gulls under one head, as they have the same generic characteristics, the only difference between them being that of size. The name of Gull applies to those species which are at least as large as Ducks; that of Mew to those which are smaller.
The Gull (Larus) and the Mew are found in every country, on every coast, out at sea, and sometimes even on fresh waters, lakes, and rivers. These birds literally swarm on some coasts, where they devour every kind of food they meet with. Fish, either fresh or stale; flesh, either fresh or decomposed; worms; shell-fish—all are alike acceptable. If these birds happen to notice the carcass of any animal, either floating on the sea or cast up on the shore, it soon becomes their prey, and is speedily devoured by these "Sea Vultures," as Buffon calls them. Should one of them discover the remains of a dead whale, or other large oceanic mammalia, it apprises the rest of the flock, and immediately they all pour down upon their booty, uttering the most discordant cries. They gorge themselves up to their very throats; but their stomachs soon digest the rapidly-decomposing animal diet. They may also be observed in search of other prey, skimming over the surface of the water, their keen eyes anxiously scanning far and near for their most favourite food, young fish.
During the breeding season they visit islands where they are sure to find thousands of eggs as well as young birds. In spite of the piteous shrieks of the parents and the plaintive cries of the young, the whole colony is sacrificed to their gluttony; the eggs are sucked, and the scarcely-hatched young ones are devoured. But, as they are always cowards, whenever these sea-vagabonds notice the approach of a bird more warlike than themselves, although, perhaps, much smaller, their only endeavour is to hide themselves, or depart with all the celerity which their long wings can give them. The mere sight of a Labbe (Stercoraria) is quite sufficient to make them disgorge their food. These birds, which are essentially water scavengers, are frequently very much in want of food, especially during stormy weather. Nature in her goodness, however, has well enabled them to endure hunger.