Mike Patterson mentioned a few references, and I'd like to add one that I
think is one of the most important books published in conservation biology
in recent years: Where Have All the Birds Gone?, by John Terborgh,
Princeton Univ. Press, 1989. Terborgh summarizes this material in his
Scientific American article, but the book contains much more. Read this
book thoroughly and you will have a good introuction to the important
questions we should be asking about bird populations, as well as knowledge
of some fascinating phenomena and individual migrant bird species in the
tropics.

Dennis Paulson
University of Puget Sound
dpaulson at ups.edu