Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/793

Rh EGGS.] BIRDS opalescence of great beauty ; but among the Tinamous (Tinainidce) colour is invariably present and their opaque eggs present the appearance of more or less globular balls of highly-burnished metal or glazed porcelain. Most birds lay eggs with a smooth shell, such as nearly all the Gavice, Limicolce, and Passeres, and in some groups, as with the normal Gfallince, this seems to be enamelled or much polished, but it is still very different from the brilliant surface of those just mentioned, and nothing like a definite line can be drawn between their structure and that in which the substance is dull and uniform, as among the Alcidce and the Accipitres. In many of the Ratitce the surface is granulated and pitted in an extraordinary man ner, 1 and in a less degree the same feature is observable in the eggs of some other birds, as the Storks (Ciconiidce). Many Water-fowls, and particularly the Ducks (Anatidce), lay eggs with a greasy or oleaginous exterior, as the col lector who wishes to inscribe his specimens with marks of their identity often finds to his inconvenience ; but there are other eggs, as those of the Anis (Crotophaga), the Grebes (Podiciptedidce), and all of the Steganopodes, except Phaeton, which are more or less covered with a cretaceous film, often of considerable thickness and varied by cal careous protuberances. of In form eggs vary very much, and this is sometimes ob servable in examples not only of the same species but even from the same mother, yet a certain amount of resemblance .is usually to be traced according to the natural group to which the parents belong. Those of the Owls (Strigidce) ,and of some of the Picarice especially those which lay the glossy eggs above spoken of are often apparently spheri cal, though it is probable that if tested mathematically none would be found truly so indeed it may be asserted that few eggs are strictly symmetrical, however nearly they may seem so, one side bulging out, though very slightly, more than the other. The really oval form, with which we are most familiar, needs no remark, but this is capable of infinite variety caused by the relative position and pro portion of the major and minor axes. In nearly all the Limicolce and some of the Alcidce the egg attenuates very rapidly towards the smaller end, sometimes in a slightly convex curve, sometimes without perceptible curvature, and occasionally in a sensibly concave curve. The eggs having this pyriform shape are mostly those of birds which invariably lay four in a nest, and therein they lie with their points almost meeting in the centre and thus occupying as little space as possible and more easily covered by the brooding parent. Other eggs as those of the Sand-Grouse (Pterodeida?) are elongated and almost cylindrical for a considerable part of their length terminating at each end obtusely, while eggs of the Grebes (Podicipedidce) which also have both ends nearly alike but pointed, are so wide in the middle as to present a biconical appearance. 2 The size of eggs is generally but not at all constantly in proportion to that of the parent. The Guillemot (Alca troile) and the Raven (Corvus corax) are themselves of about equal size ; their eggs vary as ten to one. The Snipe (Scolopax gailinago) and the Blackbird (Turdus merula) differ but slightly in weight, their eggs remarkably. The eggs of the Guillemot are as big as those of an Eagle ; and those of the Snipe equal in size the eggs of a Partridge (Perdix cinerea). Mr Hewitson, from whom these instances 1 It is curious that Ostriches eggs from North Africa are to be readily distinguished from those from the Cape of Good Hope by their smooth ivory-like surface, without any punctures, whereas southern specimens are rough as though pock-marked (Ibis, 1860, p. 74), yet no difference that can be deemed specific hi? as yet been established be tween the birds of the north and of the south. 8 A great deal of valuable information on this and other kindred subjects is given by Des Murs, Traite general d Oologie ornithclogique (8vo, Paris: 1860). are taken, remarks : &quot; The reason of this great disparity is, however, obvious ; the eggs of all those birds which quit the nest soon after they are hatched, and which are conse quently more fully developed at their birth, are very large. &quot; 3 It must bs added, though, that the number of eggs to be covered at one time seems also to have some relation to their size, and this offers a further explanation of the fact just mentioned with regard to the Snipe and the Partridge the former being one of those birds which are constant in producing four, and the latter often laying as many as a dozen for the chicks of each run as soon as they release themselves from the shell. Incubation is performed, as is well known, by the female Incubati of nearly all Birds, but with most of the Passeres and many others the male seems to share her tedious duties, and among the Ratitce, apparently without exception, the cock takes that office wholly on himself. There are a few groups or perhaps species in which the same practice is suspected to obtain certain of the Limicolai for instance, the Godwits (Limosa), the Phalaropes (Phalaropus), and the Dotterel (Eudromias morinellus] and in these it is to be remarked that the hen is larger and more brightly coloured than her mate. Owing to the unfortunate neglect of those who have the opportunity of making the needful observations the period of Incubation has been ascertained in compara tively few birds, and it is here possible to deal with that subject only in the most vague and general language. It may be asserted that most of the smaller Passeres of Europe hatch their young in about thirteen days, but in a few species the term is believed to be shortened to ten or eleven days, while in the largest of that Order, the Piaven, it is lengthened to some twenty-one days. This also is the period which the Barndoor-fowl ordinarily takes, but the Pheasant, though so very nearly allied, takes about twenty- eight. Most Water-birds, so far as is known, and the smaller Birds-of-prey seem to require as long a time, but in the Swan incubation is protracted to six weeks. The temperature of the air is commonly credited with having something to do either in hastening or retarding exclusion from the egg, but to what extent, or even whether justly so or not, seems in the absence of precise experiments to be doubtful. Certain birds occasionally begin brooding as soon as the first egg is laid, 4 and this plan unquestionably has its advantages, since the offspring being of different ages thereby become less of a burthen on the parents which have to minister to their wants, while the fostering warmth of the earlier chicks can hardly fail to aid the development of those which are unhatched, during the absence of father and mother in search of food ; but most birds, and it need scarcely be said, all those the young of which run from their birth, await the completion of the clutch before sitting is begun. The care bestowed, by almost every species, on the infant-brood, is proverbial, and there is hardly any extremity of danger which one at least of the anxious parents will not incur to ward off injury from, their pro geny. MOULT. The more or less protracted business of reproduction being ended there forthwith follows in the case of nearly all Birds a process of the most vital consequence to them. This is the Moult or shedding of their old and often wea ther-beaten feathers to be replaced by an entirely new suit. It is probably the severest strain to which bird-life is ex posed, and, to judge from. its effects on our domesticated pets, produces a greater mortality than an occasional want 3 Hewitson, op. cit. Introd. p. x. 4 This seems to be very often the case with the Owls, but if the writer s observation is not mistaken the habit is not constant even with the same individual bird.