Further Observations on Moult in the Duck Family.
[Read before the Canterbury Branch, May 3, 1938; received by the Editor. May 12, 1938; issued separately, June, 1938.]
In the interval since I wrote my last paper on this subject I have found that the principle of a double moult in the Anatidae is of much wider application than I had then thought. Since the opening of the shooting season on May 2, 1938, I have examined about thirty specimens, male and female, of Paradise Duck (Casarca variegata), and every one of them has had new contour feathers growing. In the case of the young birds, there may be very few new feathers, but birds a year or more old show a sprinkling of new feathers throughout, though in no case sufficient to give any external indication of a moult. From this two important conclusions follow:—,(1) The young birds shed their juvenal plumage, retaining their flight and tail feathers, in February, March or April, according to the original date of hatching. These birds do not moult again until the season of the post nuptial moult, when they are about one year old. (2) In the case of the Paradise Duck, the drakes as well as the ducks have a double moult, as suggested in my previous paper. Young Grey Duck (A. superciliosa) also moult their juvenal contour feathers in the autumn.
The sequence of moults shown by a tame Canada Goose (Branta canadensis) kept in my own garden may be recorded as follows:— Late in December its flight feathers began to fall, and at the end of ten days all were shed. At the same time a few of the body feathers were being moulted, but it was not until the flight feathers were nearly grown again that the body moult set in heavily. By the end of February the whole moult was complete, and I then clipped feathers on the head, neck and breast, and trimmed the light edges off the scapulars on one side of the body. Within a month the head and neck feathers were being quickly replaced with new ones, and new scapulars began to appear. This second moult is now (May 13) almost complete, there being only two or three clipped scapulars left. The cuts in the head and neck feathers are completely effaced, though a few new feathers are still coming in these parts. The goose in question is a male; but I do not doubt that the female also has a double moult.
Late in April, I caught and examined some adult White Swans (C. olor). I found new feathers, including scapulars, growing, and moulted feathers on the water, most of which were not at all frayed at the edges, I found also a few moulted feathers much frayed at the edges, indicating that they had been worn by the bird for a long time. The unfrayed moulted feathers would be post-nuptial moult feathers, and the frayed ones those assumed at
the pre-nuptial moult. The White Swan therefore also has a double annual moult. A tame Black Swan (Chenopis atrata) which I watched closely shed odd feathers throughout the autumn, indicating that it too has a double moult.
From the foregoing I think it most probable that all the members (including both sexes) of the order Anatiformes have a double moult annually, some of the feathers assumed during the post-nuptial moult being carried for a very short time (six weeks or less). It would seem also that in some cases, if not in all, the flight feathers are shed before the contour feathers, so that the theory that brilliantly coloured drakes had an inconspicuous plumage to afford them protection during their flightless period seems not to accord with the observed facts. I have seen and heard of drake mallards which were flightless yet still retained their iridescent head and nuptial body feathers. The term eclipse plumage becomes in some cases therefore a misnomer, and it would probably be better if the two plumages were referred to as post-nuptial and pre-nuptial respectively.