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Short-term oscillations in avian molt intensity: evidence from the golden eagle Aquila chrysaetos


  • David H. Ellis,

  • James W. Lish,

  • Marc Kéry,

  • Stephen M. Redpath

D. H. Ellis (correspondence), USGS Southwest Biological Science Center, Sonoran Desert Research Station, HC 1 Box 4420, Oracle, AZ 85623. E-mail: J. W. Lish, Center for Veterinary Health Sciences, Department of Physiology, Room 264 McElroy Hall, Oklahoma State University, Stillwater, OK 74079. M. Kéry, Swiss Ornithological Institute, CH – 6204 Sempach, Switzerland. S. M. Redpath, Centre for Ecology & Hydrology, Banchory, Aberdeenshire, Scotland AB31 4BW.


From a year-long study of molt in the golden eagle Aquila chrysaetos, we recorded 2069 contour feathers replaced in 137 d (6 May-19 September). Very few contour feathers were lost outside this period. From precise daily counts of feathers lost, and using time series analysis, we identified short-term fluctuations (i.e., 19-d subcycles) around a midsummer peak (i.e., a left-skewed normal distribution). Because these subcycles have never before been reported and because the physiological basis for many aspects of avian molt is poorly known, we offer only hypothetical explanations for the controls responsible for the subcycles.