Page images
PDF
EPUB

and Megaloprepia, the surface of the rami and radii is smooth and quite transparent, while between it and the pigment exists a layer of small polygonal bodies, similar to those of blue feathers.

Blue has not yet been discovered as a pigment. Blue feathers contain only orange or brownish pigment; the blue appears only on the shafts of the rami and larger radii. The structure of blue feathers seems to be always the same : (1) a transparent, colourless layer of ceratine, from 0.004 to 0.007 mm. in thickness ; (2) a layer of polygonal, more or less pyramidal, and often hexagonal columnar cells, each of which is colourless itself, and its walls are highly refractory and not unfrequently striated and ridged ;1 (3) the horny narrow cells of the inside of the radius, with brown, black, or orange pigment corpuscles.

The blue naked parts of the skin of Cassowaries contain yellow or black pigment covered by peculiarly modified epidermal layers.

III. Subjective structural, prismatic, or metallic colours. — These colours change according to the position of the light and the eye of the observer, and they always change in the order of those in the rainbow. They are restricted, as a rule, to the radii without cilia, and moreover to those parts of the feathers which are not covered by others. The metallic portions of the radii are composed of one row of compartments, which often partly overlap each other like curved tiles. In the inside black or blackish-brown pigment is collected ; and each compartment is covered with a transparent colourless layer of extreme thinness, e.g. 0.0008 mm. in Sturnus. The surface of this coat is either smooth and polished as in Nectarinia, or exhibits very fine longitudinal wavy ridges when the feather is violet, or numerous small dot-like irregularities as in Galbula. The coating seems to act like a number of prisms, as indicated in the first figure. All metallic feathers appear black when their surface is parallel to the rays of the light in the same level with the eye and the light. To the eye of the observer at A, in the lower part of the first figure, the metallic collar of Ptilorhis magnifica will appear absolutely black; the eye at B will see it bright coppery red, and at C rich green; the metallic feathers of the sides of the breast in the same bird will change from black to green at B, and to blue at C. The beautiful Pharomacrus mocinno changes from greenish bronze through golden green, green, and indigo to violet. Oreotrochilus chimborazo in position B exhibits the whole solar spectrum, namely, violet and red on the head, followed by orange and green on the back, blue, violet, and lastly purple on the

In Pitta moluccensis I calculated the following measurements : width of one polygon 0.001 mm., height of same 0.015 mm., thickness of its transparent coating about 0.0012; distance between two of the longitudinal ridges on the surface of the polygon 0.0005, thickness of the transparent outer layer of the radius about 0.005 mm.

long tail feathers. The red colours of the spectrum lie nearer towards the position A, the blue colours towards C. The colours always appear in the same order: no feathers are known, which

PositionS FOR OBSERVING THE COLOUR OF “METALLIC" FEATHERS.

(From the Proceedings of the Zoological Society, 1882.)

when looked at from B towards A, change from the red towards the blue end of the spectrum. In case two or more of these spectra (of which we imagine the horny coating to be composed) overlap each other, only a limited number of colours are able to reach the eye of the observer. Thus in the theoretical case figured red only will be visible besides black.

A peculiar case is that of Artamia bicolor; the pure white feathers

[merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small]

DIAGRAMMATIC SECTION THROUGH THE BARB OF A "METALLIC" FEATHER.

(From the Proceedings of the Zoological Society, 1882.)

of the underparts have no metallic gloss, but nevertheless they seem to be prismatic, because in position A the underparts appear bluishwhite, in B delicately pale blue, and in position C pale grey.

Deviation from the normal coloration is more or less patho

logical, and can be conveniently expressed by the term Heterochrosis (from the Greek črepos and xpwois, colouring). The following are the chief cases :

Albinism, caused by the pathological absence of the black pigment, and often locally produced by a lesion of the pulp of the growing feather; extreme instances are white Ravens and Blackbirds.

Melanism, produced by the superabundance of black pigment, mostly causing the feathers to assume a darker or more sooty colour. Melanistic specimens have been described of many birds, such as Bullfinch, Skylark, and in particular of the common Snipe, which in this phase has by some been regarded as a distinct species, Scolopax sabini.

Xanthochroism, mostly in originally red or orange feathers; when the feathers are yellow instead of green, this may possibly be a reversional step or a case of arrested development because of the absence of the green-making superstructure.

Erythrism, the abnormal occurrence of red, mostly confined to originally yellow or orange feathers, occasionally produced by abnormal food, like cayenne pepper, or directly by the colouring matter of Rubia tinctoria, one of the madder-worts. A certain correlation between green and red is exhibited by the intensely green adult males of Eclectus polychlorus, the females being bright red and the young of both sexes being reddish, without any indication of green in the young male.

In Brazil “contrafeitos” of the various species of Chrysotis are fashionable. These are produced by the rubbing in of the cutaneous secretion of a Toad, Bufo tinctorius, into the budding feathers of the head, which then turn out yellow instead of green.

Concerning the literature of Albinism and Melanism the reader may consult Toppan, Bull. Ridgway Club, 1887, pp. 61-77, and Deane, Bull. Nuttall Orn. Club, 1876, pp. 20-24; “Xanthochroism” in Parrots : Meyer, Sitzber. k. Akad. Wissensch. Berlin, 1882, pp. 517-524; and a general account by Pelzeln in Verhandl. zool.-bot. Gesellsch. Wien, 1865, pp. 911-946. For further information concerning colours see (Bronn's) Klassen und Ordn. des Thier-Reichs, Vögel, pp. 575-588, and P. 2. S. 1882, pp. 409-421, pls. 27, 28.

The distribution of colour in the feathers and the colour-pattern of the plumage require some notice.

It is a hitherto unsettled question if the longitudinally striated or the crossbarred feathers are the older style of coloration. The general impression of the coloration of a bird is the sum total of the coloration of all the uncovered parts of the feathers. This sounds like a truism, but means that crossbarred feathers can never give the general impression of a striated plumage and vice verså. Kerschner believes (Zeitschr. wiss. Zool. 1886, p. 681) that

pad, - Bufo tinced by the rubbing in of Chrysotis are

the distribution of colouring matter in transverse lines or bars is the phylogenetically older method, because natural and sexual selection cannot well have affected the hidden parts of the feathers. On the other hand, the striated downy or first plumage of the Gallina and Ratitæ has been already, by Darwin, taken to be a very old stage. This appearance, however, as in Struthio, is not due to striation of the single feathers, but to juxtaposition of colourless and deeply pigmented downs. To judge from the growth of a feather, the production of crossbars seems to be the older stage, since they will result from the intermittent deposition of pigment, while, on the other hand, the production of shaft-streaks is not yet satisfactorily explained. At any rate, it must be borne in mind that possibly various groups of birds have gone independently through such stages, and that what is primitive or archaic in one need not be so in all. But a strong proof of the soundness of Darwin's views is that we are able to trace the pattern of the most beautifully-adorned feathers of the Argus-Pheasant or of the Peacock step by step backwards to longitudinal stripes, spots, cross bars, and lastly to insignificant and simple irregular little dots.

Natural and sexual selection, whether combining or striving against each other, have worked marvels in plumage. Significant colours, as for instance total blackness or whiteness, could be developed only when higher intellectual qualities, bodily size and strength, or occasionally even special smallness, guaranteed the safety of the bird. The females and the young mostly retain a more sombre garb, and thus remain on a phylogenetically lower level. It takes the large Gulls several years to change from a mottled brownish and grey appearance into the beautifully dark and white colours. The same applies to the white shoulders of certain Eagles; and many other instances, too well known to be repeated here, shew clearly how the changes of bygone ages of the ancestors are recapitulated in the yearly moult of the growing individual until with maturity its present stage of perfection is reached—but only its present stage, because its descendants in turn will be different, either still more beautiful or still better adapted to the ever-changing conditions of life. This consideration implies that whole-coloured birds, like Swans and Ravens, have reached their limit so far as coloration is concerned ; since both black and white are very conspicuous and are correlated with a considerable amount of intellectual development. The very early assumption of the black plumage by the nestlings of Ravens and Crows is a strong argument for their relatively highest position on the hypothetical avine tree. Albinos are notoriously shy. The females of birds which breed in holes, as Rollers, Kingfishers, and Parrots, are frequently as beautifully coloured as the males, because they need no protection through colour while sitting on the nest. In the green Amazons beauty, intelligence, and safety by protection are combined. The often surprising adaptation of the coloration of the plumage to the surroundings is well known. Frequently the conspicuously coloured parts are hidden when the bird is at rest, and are only exposed or shewn-occasionally as “danger signals,” to use Mr. Wallace's excellent term—when the bird is on the wing. It cannot be doubted that the sense of colour is highly developed in birds, perhaps most so in the female when choosing a mate; the result of this sexual selection being constantly regulated by natural selection is exhibited most by the male, but enjoyed by both sexes, and for the benefit of the whole race.

COLY, Pennant's rendering of the French Coliou, adapted by Brisson from Möhring's Colius ; which, according to Cuvier, is the Greek kodolòs (see MOUSE-BIRD).

CONDOR, the Spanish way of writing the Peruvian Cuntur, the Vultur gryphus of Linnæus and Sarcorhamphus gryphus of recent authors, one of the largest of volant birds. The accounts given by early travellers of its size and ferocity were so obviously exaggerated that the cautious Ray would not admit it into Willughby's Ornithology, and only included it in his own Synopsis Avium (p. 11) after proof that such a bird existed had reached him in the shape of one of its wing-quills brought by Capt. Strong to Sir Hans Sloane from the coast of Chili. Nearly a century passed before European ornithologists saw a complete specimen. This was a female which Capt. Middleton brought from the Strait of Magellan and deposited in the Leverian Museum, where it was figured in 1791 by Shaw (Mus. Lev. No. 1, p. 4, pl.) Shortly after, a second specimen, this time an adult male, found its way from the same quarter to the same Museum, and was also figured in 1793 by the same author (op. cit. No. 6, p. 4, pl.)? But the species was little known on the continent, until in 1806 when Humboldt communicated his classical Mémoire on the bird to the French Institute, and as he was certainly the first scientific man who had made its personal acquaintance in life, his account of it deserves the attention with which it has met, and the voracity, stupidity, and tenacity of life of this huge Vulture have through him been long known to the world. Its habits have perhaps been since more fully described by Darwin in his Journal, though that account of them seems to have been unknown to the latest writer on the subject, Taczanowski (Ornithol. Pérou, i. pp. 75-80), who quotes only from D’Orbigny and Stolzmann. Yet a good many

Both these specimens passed into the Museum of Vienna, where they are now preserved (Von Pelzeln, Ibis, 1873, p. 16).

? As Broderip well remarks Molina can hardly have seen the bird, which he, like Buffon, took to be the same as the LÄMMERGEIER.

of one from the hologists saw.eton brought Museum, where sho

brought fromen.

digured in 1791eposited in the

« EelmineJätka »