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No. 49: Jan-Feb 1987

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Monarch Migration An Illusion

"The epic autumn migration of the eastern monarch butterfly to wintering grounds in Mexico, where millions cluster on trees in semi-dormancy to await spring, has become known as one of the standard 'wonders of nature' in the decade since the Mexican winter clusters were found."

There are, however, some flies in this ointment:

  1. Monarchs tagged in the north have never been found in the Mexican clusters.
  2. Fall-fattened monarchs can store only enough energy for a flight of about 200 miles -- far too short, unless they refuel along the way (no one knows if they do or not); and
  3. The monarchs seen in Mexico are almost always in pristine condition and show no wing wear or tattering.

A.M. Wenner, University of California at Santa Barbara, thinks that the "appearance" of mass migration reported frequently from many locales may just be due to a curious fall habit of the monarchs. It seems that widely scattered individuals begin to fly into the wind, and the wind concentrates and channels them to local roosts where they spend the winter. In other words, there is no long distance migration at all.

(Rensberger, Boyce; Washington Post, September 15, 1986. Cr. J. Judge)

From Science Frontiers #49, JAN-FEB 1987. 1987-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987