THE FIFTH FAMILY OF THE ZYGODACTYLE PICARIAN BIRDS.—THE WOODPECKERS (Picidæ).
These are perhaps the most typical of all the yoke-footed or climbing birds, as they are most expert climbers, being aided in the latter operation not only by their long toes, which are arranged as usual in this order in pairs, but by their stiffened tail, which enables them to climb with great rapidity up the perpendicular trunks of trees. If they wish to descend a little way they do not turn and come down head-foremost, as a Nuthatch would do, but they let themselves down by a few jerks, still keeping an oblique position, with the tail downwards. The bill in almost every member of the family is wedge-shaped, and very powerful, and with this organ a Woodpecker taps vigorously at the bark, which he sometimes also prises off to get at the grubs or insects underneath. These latter, as they endeavour to escape, have little chance against the intruder, who, in addition to the stout bill which discloses their place of concealment, possesses a peculiar tongue, which is capable of being protruded to a long distance, is furnished with minute barbs at the end, and is covered with a glutinous fluid from which the insects are unable to free themselves. The Woodpeckers nearly all procure their food in the above manner, but occasionally frequent the ground, and the Green Woodpecker (Gecinus[252]viridis) commits great ravages among ant-hills. The resting-place is generally a hole excavated by the bird itself in a hollow tree, and the eggs are white. Among the most aberrant of the Woodpecker family are the Wrynecks (Iÿnx[253]), of which one species is well known in England under the name of the “Cuckoo’s mate.” The Wrynecks are all birds of beautiful mottled plumage, and do not have a stiffened tail like a true Woodpecker. They are found in Europe, in India, North-Eastern and Southern Africa. Woodpeckers, on the other hand, are extremely plentiful in the New World, and are distributed all over Africa, Europe, and Asia, but are not found in the Australian region, no Woodpecker occurring beyond the Island of Celebes in the Moluccas.
Fig. 1.—“HYOID” BONE OF ADULT FOWL.(After W. K. Parker.)(ch) Cerato-hyals; (bh) the so-called Basi-hyal; (b.br) Basi-branchial, or Uro-hyal; (c.br,e.br) together form the thyro-hyal.
Fig. 1.—“HYOID” BONE OF ADULT FOWL.(After W. K. Parker.)
(ch) Cerato-hyals; (bh) the so-called Basi-hyal; (b.br) Basi-branchial, or Uro-hyal; (c.br,e.br) together form the thyro-hyal.
One great peculiarity in the anatomy of the Woodpeckers is the structure of the tongue, and its relation to the hyoid bone and its horns, or cornua. (For a description of this part in the Mammalia, see Vol. I., p. 168.) In Birds the hyoid bone is a much more complex structure than in the Mammalia. Besides forming the basis of the otherwise mainly muscular substance of the tongue, it is continued backwards in most birds as a double chain of bones, each pair of which bears a separate name significant of its importance; and the whole is apparently quite distinct from the skull above and from the larynx below. Its composition in the common fowl is best rendered intelligible by reference to the accompanying woodcut (Fig. 1). It represents the entire hyoid apparatus divested of all muscular and other surrounding tissues. The upper part of the figure is that nearest to the tip of the tongue, and the references to the lettering become clear in the course of the subsequent description.
Fig. 2.—SIDE VIEW OF DISSECTION OF HEAD OF COMMON GREEN WOODPECKER.(Half natural size. After Macgillivray.)(u,l) Upper and Lower Mandibles; (t) Barbed Tip of Tongue; (th.h.) Thyro-hyal Bone of Right Side, with its Muscle and Sheath; (o) Right Orbit; (n) Right Nostril; (s.g.) Right Salivary Gland; (m,m) Muscles of Neck; (œ) Œsophagus; (tr) Trachea; (r.m.) Rectractor Muscles of Tongue wound round Trachea.
Fig. 2.—SIDE VIEW OF DISSECTION OF HEAD OF COMMON GREEN WOODPECKER.(Half natural size. After Macgillivray.)
(u,l) Upper and Lower Mandibles; (t) Barbed Tip of Tongue; (th.h.) Thyro-hyal Bone of Right Side, with its Muscle and Sheath; (o) Right Orbit; (n) Right Nostril; (s.g.) Right Salivary Gland; (m,m) Muscles of Neck; (œ) Œsophagus; (tr) Trachea; (r.m.) Rectractor Muscles of Tongue wound round Trachea.
Another woodcut (Fig. 2) shows a side view of a dissection of the head of the common Green Woodpecker (Gecinus viridis), and a reference to the explanation of the lettering on it will give a general idea of the whole.
The tip of the tongue (t) is a slender, flattened, horny point, bearing on its sides and upper surface a number of very delicate bristles, or prickles, directed backwards, an arrangement eminently useful to the bird for enabling it to extract its insect food from the recesses to which its beak, by reason of its size and hardness, could not readily, nor with sufficient quickness, gain access. This tip is further rendered a more efficient instrument for this purpose by its being constantly moistened by a very viscid saliva secreted by two particularly large salivary glands (Figs. 2, 3, and 4,s.g.); and it was long ago remarked by Sir Charles Bell, in his essay on “The Hand” (Bridgewater Treatise, 1837), that the same muscles that effected the protrusion of the tongue exerted a simultaneous pressure upon these glands, so that the first result of the muscular contraction is to lubricate the tongue, while the rest of its force is spent in shooting it out with marvellous rapidity.
Fig. 3.—UPPER VIEW OF SKULL OF GREEN WOODPECKER.(After Macgillivray.)(th.h,th.h.) Thyro-hyal Bones; (i) Point of their insertion; (s.g.,s.g.) Salivary Glands.
Fig. 3.—UPPER VIEW OF SKULL OF GREEN WOODPECKER.(After Macgillivray.)
(th.h,th.h.) Thyro-hyal Bones; (i) Point of their insertion; (s.g.,s.g.) Salivary Glands.
Behind this barbed and horny tip, the tongue is a slender worm-like body, of which the core is the anterior prolongation of the hyoid bone. The fore-part of this core, more like a bristle than a bone, is known to anatomists as the “glosso-hyal,” and it is immediately succeeded posteriorly by the “cerato-hyal.”[254]Behind this is the “basi-hyal ” (Fig. 1,b.h.), the last bone to enter into the formation of the tongue proper. From this basi-hyal springs the pair of bones—the “thyro-hyals”—which attain the remarkable degree of development for which the birds now under consideration are distinguished. From each side of the hinder portion, then, of this basi-hyal bone diverge these important “thyro-hyals” (Fig. 1,c.br.,e.br.). They, in the Woodpeckers (compare Fig. 3,th.h.), extend outwards and backwards to pass one on each side of the neck until they curl upwards and forwards, converging to meet one another on the upper part of the back of the head; thence they run along together, ploughing themselves a furrow in the skull-top till they reach almost to the right nostril. Each of these curved and highly elastic bones is surrounded by a delicate sheath, whose inner surface is kept constantly moist and lubricated by its own secretion; and this sheath is attached to the bone of the skull at its junction with the upper mandible, as is shown in the accompanying woodcut (Fig. 3,i).
Fig. 4.—DISSECTION OF HEAD OF GREEN WOODPECKER VIEWED FROM BELOW.(After Macgillivray.)(l) Lower Mandible; (f) Base of Tongue; (th.h.,th.h.)Thyro-hyals; (s.g.,s.g.) Salivary Glands; (m,m) Muscles of Neck; (œ,œ) Œsophagus; (tr) Trachea; (e.m.,e.m.) Extrusor Muscles, which thrust out the Tongue; (r.m.) Retractor Muscles of Tongue wound round Trachea; (c.tr.,c.tr.) Cleido-tracheal Muscles, binding Trachea to Shoulder-girdle.
Fig. 4.—DISSECTION OF HEAD OF GREEN WOODPECKER VIEWED FROM BELOW.(After Macgillivray.)
(l) Lower Mandible; (f) Base of Tongue; (th.h.,th.h.)Thyro-hyals; (s.g.,s.g.) Salivary Glands; (m,m) Muscles of Neck; (œ,œ) Œsophagus; (tr) Trachea; (e.m.,e.m.) Extrusor Muscles, which thrust out the Tongue; (r.m.) Retractor Muscles of Tongue wound round Trachea; (c.tr.,c.tr.) Cleido-tracheal Muscles, binding Trachea to Shoulder-girdle.
Enclosed in the sheath here spoken of, and along the concavity of each bone, is a muscle which has a fixed attachment to the crura of the lower mandible on each side (Fig. 4,e.m.,e.m.). The contraction of this muscle shoots the tongue out in two different ways. In the Green Woodpecker the extremities of the thyro-hyal bones are themselves attached to the mandible, while the curvature of the bones makes a loop that hangs low down on each side of the neck (see Fig. 2,th.h.). As the muscle is shortened this loop is raised up, and the free tip of the tongue is consequently projected; and since the muscle is on the inner, or concave, side of the curve, a very small shortening on its part makes a great addition to the apparent length of the tongue. Sir Charles Bell elucidates this action by comparing the great effect on the curve of a fishing-rod’s flexible top that a small tightening of the line has. But while this is the case in many species, there are others in which the sheath alone is attached to the bones of the forehead, and the bones themselves slide along inside together with the contracting fibres of the muscle, thus producing the same result as was obtained in the other case by the loops hanging low down in the neck.
The tongue, whose length is thus so extraordinarily increased, is drawn back to its original position within the bill by another pair of muscles, one on each side, which are attached to the basi-hyal. These take their origin from the trachea, around which (as shown in Figs. 2 and 4,r.m.), in many species, they are curiously wound in their course. And, since the bones are at the point of their greatest curvature when at rest, it is obvious that this action of withdrawal is materially assisted by the elasticity of the prolongations of the hyoid bones themselves; for it is a well-known law that Nature never lets power run to waste, but always utilises forces of mere elasticity or rigidity when by their means the expenditure of nervous energy and muscular contractility can be saved.
WRYNECK.
WRYNECK.
It may be observed that this curious development of the bones of the tongue is not confined to the Woodpeckers; in the Sun Birds (Nectariniidæ) of the Old World, and the Humming-Birds (Trochilidæ) of the New, this same adaptation of means to ends obtains. Even in the Picidæ themselves many variations have been noticed, in addition to those above alluded to; for instance, in the Yellow-billed Woodpecker (Sphyrapicus[255]varius) of North America the horns of the hyoid do not reach so far as the eye, so that the tongue, with its bushy tip in this case, is only extensible in a very slight degree; while in the Hairy Woodpecker (Picus villosus) the thyro-hyals curve spirally over the right orbit so as to reach entirely around the eye, to be inserted at its lower posterior margin.
GREAT BLACK WOODPECKER AND GREAT SPOTTED WOODPECKER.⇒LARGER IMAGE
GREAT BLACK WOODPECKER AND GREAT SPOTTED WOODPECKER.
⇒LARGER IMAGE
Considerable difference of opinion exists as to the damage done by Woodpeckers in tapping sound trees, and many a poor bird pays the penalty of his life for his supposed destructive propensities. Mr. Waterton argues strongly on the side of the bird, and alleges that only rotten and unsound trees are attacked for the sake of a nesting habitation, or for the purpose of getting insects; but that this is not always the case was proved by the writer himself in the spring of 1878, when a boy was sent up to a hole in a beech-tree in Avington Park, in Hampshire. The tree was stillperfectly sound, so sound, indeed, that the bird had evidently given up the idea of inhabiting it for that year, and had betaken himself elsewhere, after having excavated a round hole to the depth of two or three inches. In the same tree, a little lower down, was a similar hole, evidently made the previous year, when the bird had “tapped” the tree, and it was clear that he had returned again in the succeeding season, and had tried a little higher up in the trunk, to see if there were any chance of procuring a domicile. This proceeding must have injured the tree, and was the work of a Green Woodpecker, or Yaffle, whose laughing note was heard from another quarter of the park, even as the above examination was being conducted. In this part of Hampshire, though the bird is not persecuted by the owner of Avington, Mr. Edward Shelley, or by his keepers, the Green Woodpecker is rare; but in certain parts of Huntingdonshire the writer can remember to have found it very plentiful in his school-days, and it was a never-failing object in a country walk, flitting from tree to tree in front of the observer, and always keeping a sharp look-out from the opposite side of the trunk on which he settled. This species appears in old pieces of poetry under the various names of Yaffle, Woodwele, or Woodwale, Whetile, and it is in some places called “Hewhole,” Woodhacker, &c.[256]:—
GREEN WOODPECKER.
GREEN WOODPECKER.
“The Skylark in ecstasy sang from a cloud,And Chanticleer crowed, and the Yaffil laughed loud.”The Peacock at Home.
“The Skylark in ecstasy sang from a cloud,And Chanticleer crowed, and the Yaffil laughed loud.”The Peacock at Home.
“The Skylark in ecstasy sang from a cloud,And Chanticleer crowed, and the Yaffil laughed loud.”The Peacock at Home.
“The Skylark in ecstasy sang from a cloud,
And Chanticleer crowed, and the Yaffil laughed loud.”
The Peacock at Home.
“The Woodwele sang, and would not cease,Sitting upon the spray;So loud he wakened Robin HoodIn the greenwood where he lay.”Ritson’s Edition ofRobin Hood, vol. i., p. 115.
“The Woodwele sang, and would not cease,Sitting upon the spray;So loud he wakened Robin HoodIn the greenwood where he lay.”Ritson’s Edition ofRobin Hood, vol. i., p. 115.
“The Woodwele sang, and would not cease,Sitting upon the spray;So loud he wakened Robin HoodIn the greenwood where he lay.”Ritson’s Edition ofRobin Hood, vol. i., p. 115.
“The Woodwele sang, and would not cease,
Sitting upon the spray;
So loud he wakened Robin Hood
In the greenwood where he lay.”
Ritson’s Edition ofRobin Hood, vol. i., p. 115.
“There the Jay and the ThrostellThe Mavis menyd in her song,The Woodwale fard or beryd as a bellThat wode about me rung.”True Thomas.
“There the Jay and the ThrostellThe Mavis menyd in her song,The Woodwale fard or beryd as a bellThat wode about me rung.”True Thomas.
“There the Jay and the ThrostellThe Mavis menyd in her song,The Woodwale fard or beryd as a bellThat wode about me rung.”True Thomas.
“There the Jay and the Throstell
The Mavis menyd in her song,
The Woodwale fard or beryd as a bell
That wode about me rung.”
True Thomas.
Some Woodpeckers seem to make storehouses against the winter, by pecking holes in a tree, and an interesting example of a piece of bark, in which a Red-headed Woodpecker (Melanerpes formicivorus)[257]had placed a store of acorns, is to be seen in the British Museum.
Another British species, the Lesser Spotted Woodpecker (Picus[258]minor), is a bird of different habits, frequenting fruit-gardens in the autumn, and doing very little damage to trees in the nesting season. It generally selects the rotten branch of an old poplar-tree, and hollows out a hole in so perilous a situation that it is difficult to climb to, and, indeed, the whole bough is often brought down by the first gale in the ensuing winter. Here its small wedge-shaped bill speedily makes an excavation, and at some little distance down in the hollow interior it lays its glossy white eggs on the touchwood and decaying wood. Both sexes assist in the preparation of the nest; and in mild winters they sometimes begin with the commencement of the year to look out for their future home. The selection of this appears to be a matter of no small anxiety, for several trees are examined in turn, and often at long distances apart. The birds at the time of incubation keep up a continual signalling one to the other, which is produced by a rapid whining noise caused by tapping on the thinner branches of the dead trees. This call-note, if it may be called such, is generally heard in the early morning, and ceases as soon as the nesting operations have finally commenced. Besides this note, they have also one like the “laugh” of the Green Woodpecker, but, of course, much reduced in accordance with the difference in the size of the two birds. The little Spotted Woodpecker may often be seen hanging on to, and climbing round, the slender twigs of the outer branches of a tree, and looks much like a Creeper or a Nuthatch, which it does not greatly exceed in dimensions.