SHELD-DRAKE, or, as commonly spelt in its contracted form, SHELDRAKE, a word whose derivation has been much discussed, one of the most conspicuous birds of the Duck tribe, Anatidx, called, however, in many parts of England the "Burrow-Duck" from its habits presently to be mentioned, and in some districts by the almost obso-lete name of " Bergander" (Dutch, Berg-eende, Germ. Berg-ente), a word used by Turner in 1544.

The Sheldrake is the Anas tadorna of Linnaeus, and the Tadorna comuta or T. vulpanser of modern ornithology, a bird somewhat larger and of more upright stature than an ordinary Duck, having its bill, with a basal fleshy protuberance (whence the specific term comuta), pale red, the head and upper neck very dark glossy green, and beneath that a broad white collar, succeeded by a still broader belt of bright bay extending from the upper back across the upper breast. The outer scapulars, the primaries, a median abdominal stripe, which dilates at the vent, and a bar at the tip of the middle tail-quills are black ; the inner secondaries and the lower tail-coverts are grey ; and the speculum or wing-spot is a rich bronzed-green. The rest of the plumage is pure white, and the legs are flesh-coloured. There is little external difference between the sexes, the female being only somewhat smaller and less brightly coloured. The Sheldrake frequents the sandy coasts of nearly the whole of Europe and North Africa, extending across Asia to India, China, and Japan, generally keeping in pairs and sometimes penetrating to favourable inland localities. The nest is always made under cover, usually in a rabbit-hole among sand-hills, and in the Frisian Islands the people supply this bird with artificial burrows, taking large toll of it in eggs and down. Barbary, south-eastern Europe, and Central Asia are inhabited by an allied species of more inland range and very different coloration, the T. casarca or Casarca* rutila of ornithologists, the Ruddy Sheldrake of English authors—for it has several times strayed to the British Islands,—and the " Brahminy Duck" of Anglo-Indians, who find it resorting in winter, whether by pairs or by thousands, to their inland waters. This species is of an almost uniform bay colour all over, except the quill-feathers of the wings and tail, and (in the male) a ring round tho neck, which are black, while the wing-coverts are white and the speculum shines with green and purple ; the bill and legs are dark-coloured. A species closely resembling the last, but with a grey head, T. cana, inhabits South Africa, while in some of the islands of the Malay Archi-pelago, and in the northern parts of Australia, there is a fourth species, T. radjah, which almost equals the true Sheldrake in its brightly contrasted plumage, but yet wants some of the lively colours the latter displays—its head, for instance, being white instead of dark green. Further to the southward in Australia occurs another species of more sombre colours, the T. tadornoides; and New Zealand is the home of a sixth species, T. variegata, still less distinguished by bright hues. In the last two the plumage of tho sexes differs not inconsiderably, but all are believed to have essentially the same habits as the T. cornuta.





It is not without a purpose that these different species are here particularized. Sheldrakes will, if attention be paid to their wants, breed freely in captivity, crossing if oppor-tunity be given them with other species, and an incident therewith connected possesses an importance hardly to be overrated by the philosophical naturalist, though it seems not to have met with the attention it deserves. In the Zoological Society's gardens in the spring of 1859 a male of T. comuta mated with a female of T. cana, and, as will have been inferred from what has been before stated, these two species differ greatly in the colouring of their plumage. The young of their union, however, presented an appear-ance wholly unlike that of either parent, and an appearance which can hardly be said, as has been said (P. Z. S., 1859, p. 442), to be "a curious combination of the colours of the two." Both sexes of this hybrid have been admirably por-trayed by Mr Wolf (torn, cit., Aves, pi. 158); and, strange to say, when these figures are compared with equally faith-ful portraits by the same master (op. cit., 1864, pis. 18, 19) of the Australian and New Zealand species, T. tadornoides and T. variegata, it will at once be seen that the hybrids present an appearance almost midway between the two species last named—species which certainly had nothing to do with their production. The only explanation of this astounding fact seems to be that afforded by the principle of "reversion," as set forth by Mr Darwin, and illustrated by him from examples of certain breeds of Doves, domes-tic Fowls, and Ducks (Anim. and PI. under Domestication, i. pp. 197-200, ii. p. 40), as well as, in the matter of domestic Fowls, by Mr Cambridge Phillips (Zoologist, 1884, p. 331). It is a perfectly fair hypothesis that the existing animals of New Zealand and Australia retain more of their ancestral character than do those of countries in which we may suppose the struggle for life to have been fiercer and the action of natural selection stronger. Why it is so we cannot say, yet experiment proves that the most widely different breeds of Pigeons and other poultry, when crossed, produce offspring that more re-sembles the ancestral wild species from which the domestic-ated forms have sprung than it resembles either of the immediate parents. This mysterious agency is known as the principle of "reversion," and the example just cited proves that the same effect is produced in species as well as in "races,"—indicating the essential identity of both, —the only real difference being that " species " are more differentiated than are "races," or that the distinction between them, instead of being (as many writers, some of the first repute, have maintained) qualitative, is merely quantitative, or one of degree.

The genus Tadorna, as shewn by its tracheal characters, seems to be most nearly related to Chenalopex, containing the bird so well known as the Egyptian Goose, C. aegyptiaca, and an allied species, C. juhata, from South America. For the same reason the genus Plectropterus, composed of the Spur-winged Geese of Africa, and perhaps the Australian Anseranas and the Indian and Ethiopian Sarcidiornis, also appear to belong to the same group, which should be reckoned rather to the Anatine than to the Anserine section of the Anatidse. (A. N.)





Footnotes

4 Bonaparte was pleased in 1838 to separate this species from the genus Tadorna, but neither he nor any of his successors has shewn any good reason for doing so.

5 Jerdon (B. India, iii. p. 793) tells of a Hindu belief that once upon a time two lovers were transformed into birds of this species, and that they or their descendants are condemned to pass the night on the opposite banks of a river, whence they unceasingly call to one another: " Charkwa, shall I come ?" "No, Charkwi." " Charkwi, shall I come ? " "No, Charkwa." As to how, under these circumstances, the race is perpetuated the legend is silent.



The above article was written by: Prof. Alfred Newton.