Part 8

CLASS II.: =AVES= (BIRDS).

Warm-blooded Vertebrates, which breathe by lungs, are covered with feathers, have no teeth but a horny beak, and lay hard-shelled eggs, which are hatched by the warmth of their body. They are adapted for movement in the air, though not all to the same degree. The fore limbs are modified into wings, in which, however, the parts found in Mammals can be recognized. We distinguish in the first place a small thumb, and then in most cases a two-jointed forefinger and a small second finger. Secondary quills (Fig. 28, BB) are attached to the ulna, and primary quills (A, 1–10) to the two metacarpals and the finger joints, while the thumb bears the bastard wing (C). The tail feathers, or rectrices, are attached to the last joint of the tail. The body is clothed with stiff, tolerably long contour feathers, which conceal the soft short down from view. The bones are hollow and filled with air. Their cavities are connected with air-sacs, which are found in all parts of the body, and fill themselves with air from the lungs when the bird begins to fly. In this way its specific gravity is reduced. The body firm, especially the hinder part of it, which is almost immovable; the neck, which may consist of many vertebræ (even as many as twenty-two), can, on the contrary, be turned in many directions. Birds walk entirely on their toes; the metatarsals are fused with one of the rows of tarsals into a “tarsus” bone. Tarsus and toes are covered with horny scales.

A bird’s egg (Fig. 29) consists of a germinal disc (h) from which the young bird develops, and which rests on the yolk, made up of substances serving for the nutriment of the developing bird: the yellow (a) and the white (b) yolk, as well as the albumen (c, c^1, “white of egg”) in which lie two twisted cords (chalazæ),—finally of protective structures: the shell-membrane (e) and the calcareous shell (f); g is the air-chamber.

FIG. 28.—Wing of the Buzzard. ]

FIG. 29.—A Bird’s Egg. ]

When the young escape from the egg, they are either able to at once look after themselves more or less, at least to look for their food,—in which case they can see and are clothed with feathers at hatching (precocious young; e.g. fowls, ducks, gulls, and pewits),—or the young remain some time in the nest, as they are, to begin with, both blind and naked, and in this case they are fed for some time by the parents (nestlings; e.g. birds of prey, sparrows, nightingales, pigeons). In the frigid and temperate zones most species of birds do not remain in their native country after the breeding season; those which go south in the autumn are termed migrants; while birds which do not migrate, but remain in the district where they have bred, are known as residents (sparrow, jay, magpie). Gipsy migrants execute more or less extensive wanderings, influenced by want of food or other causes (woodpecker, titmouse, golden-crested wren, tree-creeper). The travels of such birds are not, like those of migrants, undertaken at a definite time of year, or in definite directions (N., S.), but many of their species collect together in large flocks for the purpose of wandering, like migrants.

The following orders are usually distinguished:

FIG. 30.—The Eagle Owl (Otus maximus). ]

I. Raptores (Birds of Prey), II. Scansores (Climbers), III. Passeres (Singing Birds), IV. Gyrantes (Doves), V. Rasores (Scratchers), VI. Grallatores (Waders), VII. Natatores (Swimmers), VIII. Cursores (Running Birds).

The Order Cursores includes the ostrich-like birds, and will not here receive further notice.

ORDER: Raptores (BIRDS OF PREY).

Upper beak hooked, covered with a skin (cere) at its base; four toes possessing strong claws, and provided with pads in their under side (Fig. 31); wings powerful. Birds of prey live in pairs, and breed once a year in nests composed of pieces of wood and branches. The young are nestlings (p. 51). Sight keen. These birds feed almost exclusively on vertebrates, principally mammals and birds. An idea of their food can be gained by examination of their “pellets”—roundish balls composed of the indigestible parts of their food, and disgorged from twelve to twenty hours after feeding. Two groups are distinguished—diurnal and nocturnal birds of prey. The first (Figs. 31, 32) have a laterally flattened head, eyes directed laterally, and tolerably stiff feathers. The nocturnal forms (“owls,” Figs. 30, 33) have a large head, flattened in front, with large eyes facing to the front, soft plumage, and hair-like feathers on the toes, of which two are directed forwards, one backwards, and one outwards. The radiating feathers round the eye constitute a “veil.”

FIG. 31.—Head and Foot of Falcon. ]

Predominatingly harmful (from killing domestic mammals) are the following species occurring in Britain: the =Sea Eagle= (Haliaëtus albicilla), the =Golden Eagle= (Aquila chrysaëtus), the =Peregrine Falcon= (Falco peregrinus), the =Merlin= (F. œsalon), the =Hobby= (F. subbuteo), the =Sparrow Hawk= (Accipiter nisus), the =Kite= (Milvus regalis), the =Goshawk= (Astur palumbarius), the =Harriers= (Circus cyaneus and C. cinerarius), and the =Honey Buzzard= (Pernis apivorus). The last effects damage by catching honey bees.

FIG. 32.—The Golden Eagle (Aquila chrysaëtus). ]

Useful in the main, being destroyers of field-voles, are the following: the =Kestrel= (Falco tinnunculus), the =Buzzard= (Buteo vulgaris), the =Barn Owl= (Strix flammea, Fig. 33), the =Brown Owl= (S. aluco), the =Little Owl= (Athene noctua), a casual, the =Short-eared= or =Woodcock Owl= (Otus brachyotus), the =Long-eared Owl= (O. vulgaris), and the =Eagle Owl= (Otus maximus, Fig. 30), a rare visitor.

A bird of prey cannot simply be classed as harmful or useful; a species mainly injurious may sometimes destroy a field vole or a destructive bird, while a useful species may sometimes attack domestic poultry. Game-preserving is destructive of almost all the indigenous diurnal birds of prey, and of the owls to a less extent.

ORDER: Scansores (CLIMBERS).

Birds with two toes directed forwards and two backwards. The young are nestlings. Here belong toucans, parrots, cuckoos, and woodpeckers. The first two groups are limited to the tropics; woodpeckers are only of importance in the culture of fruit trees and in forestry. I describe briefly—

FIG. 33.—The Barn Owl (Strix flammea). ]

The =Cuckoo= (Cuculus canorus, Fig. 34). Fourteen inches long, tail eight inches. The yellowish beak is slightly curved; feet yellow. Back blue-grey in old birds, brownish in young ones. Belly white with dark transverse lines. Ten tail quills, flecked with white. Shy; flies like a bird of prey. The female lays her eggs at intervals of about fourteen days, and cannot therefore hatch them out herself. She lays the egg on the ground, and then takes it in her bill to the nest of a small bird which feed its young with insects (wagtail, grasshopper warbler, nightingale, robin, lesser whitethroat, wren, lark). The cuckoo’s egg is generally hatched by the foster parent, and the true young often do not come out from the egg, owing to lack of warmth; or, if hatched, they are thrown out later on by the much larger, rapidly developing young cuckoo. Every cuckoo, therefore, is so far harmful that it costs the lives of several insect-eating birds. But it far more than compensates for this by destroying insects. It is especially beneficial to fruit-tree culture and forestry, since it eats an enormous number of caterpillars; but in late summer it comes frequently from the woodland into the fields, and then eats the caterpillars of the cabbage white, cabbage moth, and silver Y moth, surface caterpillars, and the larvæ of the turnip saw-fly. It also devours mole-crickets and (naturally in the spring) cockchafers.

FIG. 34.—The Cuckoo (Cuculus canorus). ]

ORDER: Passeres (PERCHING BIRDS).

This order is essentially constituted by all those birds with helpless young (p. 51), which do not belong to the two preceding orders or the one next following. Beak without a cere. Three toes forwardly, one backwardly directed.

Group: =Hirundinidæ= (Swallows).

With short flat beak, broad at the base, with gape extending far back, and triangular as seen from above. In flight the beak is opened as widely as possible, serving for catching insects. Wings long and pointed. Feet short and weak, entirely unsuited or only poorly adapted for walking; their chief use is to enable the swallow to hold fast to different objects. Swallows fly quickly and catch insects while on the wing. The insects on which they prey are generally unimportant to agriculture and forestry; but they may also do good by catching crane flies (Tipula), and ribbon-footed corn flies (Chlorops), which often fly about our fields in enormous swarms in order to lay their eggs. All swallows are migratory birds. There belong here—

1. True =Swallows= (Hirundo), with forked tails; three toes directed to the front, one to the back. Here may be reckoned—=Swallow= (H. rustica), always broods in sheltered spots, e.g. inside a stable, summer-house, or verandah; =House Martin= (H. urbica), nests against buildings, under the eaves for example; the =Sand Martin= (H. riparia), breeds in the neighbourhood of streams, especially in vertical banks of loamy or coherent sandy soil, where it makes its nest at the end of a passage a yard long. The =House Martin= is shining black on the back, white on the entire under surface and rump. The =Bank Martin= is brownish grey on the back, white on the under side, with brownish-grey bands on the breast.

2. =Swifts= (Cypselus), with forked tails and four strong, curved, forwardly directed claws. Only one British species belongs here—the =Swift= (Cypselus apus), ten inches long, brownish black except for white throat, and with very long curved wings.