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How Birds Molt
BY JONATHAN DWIGHT. JR.. MD.
N spite of much that has been written in the past about the molting I of birds, the subject is by no means threadbare. and I hope that a brief sketch of the complicated process of feather-renewal will stimulate interest in its further study. Periodically, old plumage is cast aside feather by feather as new ones grow, and so gradually does this take place that most birds are able to fly about as if nothing unusual were in progress. Many species (among them the Thrushes, Wrens, Blackhirds. Jays, Woodpeckers. Hawks. Owls, and a few others) wear only one plumage throughout the year, exchanging the more or less ragged remains for a fresh suit at the end of the breeding season; while many Warblers, Sparrows, \Vaders and others molt part of their body plumage a second time in the winter or spring. These two molts are the postnuptial and the prenuptial, giving distinctive winter and summer pluinages.
Two plumages are peculiar to young birds—first, the natal, the stage of soft. downy baby-clothes, and, second. the juvenal or knickerbocker stage, The weak, juvenal feather of a young Purple Finch is shown by the half-tone which is from a photornicrograph. Both plumages of young birds vary greatly in different species We are familiar with the little tufts of natal down scattered on nestling Sparrows. Thrushes, or \Varblers, and the dense covering of Ducklings. Gulls, Game»birds or Hawks and Owls. In Woodpeckers it is aborted.
The juvenal plumage. delicate and transient in most land birds, may be worn wholly or in part for many months in large species, and is often confused with other plumages. If. however, we bear in mind that there is nothing haphazard in the growth of feathers and the sequence of melts and resulting plumages, our ideas upon the subject will become very much clearer. At a definite time and at a definite point of the skin, each and every feather grows. and plumages are only successive generations of feathers.
Abrasion. attrition and weathering of feathers go to make up wear which sometimes produces surprising color»changes in plumages, The loss of the brown feather edgings of. for instance. the fall Snowflake or Redrwinged Blackbird. displays the black hidden beneath, and the loss of the little barbules of the feathers of Crossbills or of the pink Purple Finch brightens red colors by subtracting the gray tints, The first
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