AN ALTITUDINAL CLINE IN CONDUCTANCE OF CLIFF SWALLOW (PETROCHELIDON PYRRHONOTA) EGGS TO WATER VAPOR

American Cliff Swallow (Petrochelidon pyrrhonota) Science Article 1

abstract

The rate of diffusion of water molecules through air is inversely related to atmospheric pressure; diffusivity of water vapor, therefore, is greater at high altitudes than at lowelevations. Assuming that conservation of water in avian eggs is essential for normal development and hatching of embryos, we predicted that eggs laid by birds nesting at high altitudes would have lower conductances to water vapor under standard conditions than eggs laid by conspecifics nesting at low elevations, thereby compensating for the increased potential for transpirational water loss from eggs at high altitudes

PAUL R. SOTHERLAND, The Auk 97: 177-185. January 1980

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