Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/794

776 of proper or even any food does. Important however as are its bearings on every individual of the whole Class, the subject is one which has been sadly neglected by ornitho logical writers and, with one exception, we are not aware of any connected series of observations on Moult within the whole range of their literature. The structure and mode of growth of feathers has been very well studied and de scribe:! by several investigators, and must be especially treated in introducing the subject of Pterylography or the disposition of the various plumed patches on the bird s body which, having been found to be a most useful auxili ary in Classification, is deferred until that comes to be discussed under the article &ldquo;.&rdquo; For the present we have briefly to consider the different phases which the process of Moulting offers.

As a general rule all Birds are subject to an annual Moult, and this as above stated, commonly begins immedi ately 0:1 the close of the breeding-season, but, as will be explained further on, there are some which undergo in addition a sooond or even a third partial change of plum age, and it is possible that there may be others still more exceptional, our information respecting these, however, is too meagre to make it worth while saying anything here about thorn. It must be acknowledged that with regard to the groat majority of forms we can only judge by analogy, and though it may well be that some interesting deviations from the general rule exist of which we are altogether ignorant, yet when we consider that the Ratita:, so far as observed, moult exactly in the same manner as other birds, the uniformity of the annual change may be almost taken for granted.

It is not intended here to describe the way in which a feather dies and a new one succeeds it, nor need we compare the process of moulting with the analogous shedding of the i ia i r m Mammals or of the skin in Reptiles. Enough for our present purpose to see that such renovation is required in Birds, which nearly all have to depend upon their quills for the means of locomotion and hence of livelihood. It is easy to understand that durable as are the flight-feathers, they do not last for ever and are besides very subject to accidental breakage, tho consequence of which would be the crippling of the bird. It is obviously to provide against what in most cases would be such a disaster as this last that we find the remiges, or quill-feathers of the wings, to be always shed in pairs. They drop out not indeed abso lutely at the same moment, though this sometimes seems to happen, but within a few days of each other, and, equilibrium being thus preserved, the power of flight is Taut slightly deteriorated by their temporary loss. The same may be observed in a less degree, since there is less need of regularity, with the rest of the plumage, as a little attention to any tame bird will show, and the new feathers grow at an almost equal rate. In the young of most species the original quills are not shed during the first year, nor in the young of many does there seem to be an entire moult during that time, but in the typical Galliiice, which are able to fly at a very early age, often before they are one-third grown, the original quills, being proportioned to the duties required of them, are shed before the bird has attained its full size and are succeeded by others that serve it when it has reached maturity. In the Duck-tribe (Anatidce), however, we have a very singular exception to what has been above stated. Most of these birds shed their quill- feathers all at once, and become absolutely incapable of flight for a season, during which time they generally seek the shelter of thick, aquatic herbage, and it is further to be particularly remarked that the males of most of two sections of the family (Anatince and Fuligulince) at the same period lose the brilliantly-coloured plumage which commonly distinguishes them ajid &quot;go into eclipse,&quot; as &quot;Waterton happily said, putting on for several weeks a dingy garb much resembling that of the other sex, to resume their gay attire only when, their new quills being grown, it can be safely flaunted in tho open air. Here we have the first instances of Additional Moult to be mentioned. Another is not less interesting, though ornithologists must confess with shame that they have not sufficiently investigated it. This is that of the Ptarmigan (Lagopus mutus), both sexes of which not only moult after the breed ing-season is over into a grey suit, and then again as autumn passes away into their snowy winter-clothing, but, divesting themselves of this last in spring, then put on each a third and most distinctive dress these changes, however, do not extend to the quills either of the wings or tail.

The number of Birds which undergo a more or less entire Double Moult is very considerable, and the peculiarity is not always characteristic of families or even, unless in a a restricted sense, of genera. Thus while the Garden-Warbler (Sylvia salicaria] is said to moult twice in the year the Blackcap (S. atricapilla) does so but once. The same may be said of the Emberizidae, in which family both practices seem to obtain, but on the other hand the distinction in this respect between the Larks (Aland idee) and the Pipits (Anthiiice), belonging to the family Motacillidcc, appears, so far as our knowledge goes, to be invariable, though the habits and general appearance of both groups are so much alike the AlandidcK moulting but once and the Anthince, conform ing to the practice of the normal Motacillidce (Motacillince), twice a year the quills, be it understood, excepted. But it would be impossible here to give more than these few examples, and indeed we scarcely know anything of the subject outside of groups belonging to the Northern hemisphere.

In a large number of species the Additional Moult is very partial, being often limited to certain portions of the plumage, and it is yet an unsolved problem how far some of the changes to be observed are due to actual Moult and how far to the alteration of colour in the feathers themselves, as also the way by which this alteration of colour is produced, whether, as certainly happens in many instances, by the dropping off of the &quot; barbicels &quot;the fine filaments that fringe the &quot; barbicels &quot; which are arranged on the upper surface of each &quot; barb &quot; composing the web of the feather or in some other manner, iti either of these last considerations we need not now concern ourselves. It is unquestionable that there are innumerable species of birds, the males at least of which put forth in spring decorative plumes unknown at any other season, and it would appear that in the majority of them the feathers which before clothed the parts whence the newly -donned ornaments grow are doffed to make room for these paraphernalia of marriage. The subject of Additional Moult is thus intimately con nected with the seasonal adornment of Birds, and as that 