The Mechanism of Feather Replacement during Natural Molt

MOST ornithological reference books state that natural molt is a twopart process entailing loss of old feathers, "ecdysis," and subsequent growth of new feathers, "endysis" (Stresemann, 1927; Mayaud, 1950; Wing, 1956; Van Tyne and Berger, 1959).Furthermore, investigators who have studied molt in penguins, cassowaries, and emus state or imply that they are aberrant, since, in these birds, the old feathers are pushed out attached to the tips of the feathers of the incoming generation and are later abraded or are pulled off by the bird (Bartlett, 1879;Lowe, 1933;Friedmann, 1949;Rand, 1950).The evidence to be presented in this paper, very briefly reported earlier by Watson ( 1963), indicates, however, that this latter mechanism of feather replacement is more widespread among birds than previously believed and that natural molt is actively concerned only with the incoming generation.This finding is of signifi-Oct.I W^rso>;, Feather Replacement 487 1963 birds were handled daily and examined for molt while they were developing.All juvenal feathers dropped by one chukar were collected every other day.Nonliving material consisted of five birds.An adult male Chukar Partridge, which died while molting at the Highland Park Zoo in Pittsburgh, and an adult male House Sparrow (Passer domesticus), picked up dead in Arlington, Virginia, were examined in the flesh.Flat skins of two molting Greater Scaup ducks (Aythya marila) were examined immediately after preparation.A wild Ruddy Sheld-Duck (Casarca ferruginea), preserved in formalin in 1960, was studied two years later.Molting feathers were examined and photographed, when possible, on the living bird.Others were plucked, and examined or dissected while fresh, under a binocular dissecting microscope.A few molting feathers were preserved in Bouin's or Carnoy's fluids and examined after fixation.In order to investigate growth rate during the development of early feather generations, Richard J. Hart, a student at Yale University, made daily measurements under my direction on the innermost primary (number I) in female "Hall Cross" Rhode Island red preserved embryos and living chicks.For each day of incubation (days II through 20) he measured at least five specimens.Five chicks were raised for 32 days under the same conditions as the other live birds under observation.Measurements taken with calipers on the visible portion of the feather were recorded to the nearest 0.I mm in the embryos and 0.5 mm in the live chicks.