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A Study of Autumnal Postmigrant Weights and Vernal Fattening of North American Migrants in the Tropics

David T. Rogers, Jr. and Eugene P. Odum
The Wilson Bulletin
Vol. 78, No. 4 (Dec., 1966), pp. 415-433
Stable URL: http://www.jstor.org/stable/4159532
Page Count: 19
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
A Study of Autumnal Postmigrant Weights and Vernal Fattening of North American Migrants in the Tropics
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Abstract

The autumnal arrival weights in Panama and vernal fattening in British Honduras were studied for several species of trans-Gulf migrants. Birds arriving in Panama were extremely thin and many were below the estimated fat-free weights for the species. Fat indices on some specimens which were extracted, were below any which have been reported previously in the literature. Evidence is presented that fat-free weight may have been used as an energy source in some postmigrants. The premigratory buildup of fat reserves in Catbirds, Orchard Orioles, Indigo Buntings, and Yellowthroats in British Honduras indicated that some individuals of these species attained trans-Gulf flight capabilities at different dates while the fattening of sexes differed by date in the Orchard Oriole. The possibility that Stann Creek Valley may be a final stop in Central America for some species during spring is discussed. Data on weight changes in recaptured birds indicated that weight losses between capture dates may have been caused by handling of the birds.

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