Tolerance of Variation in Eggshell Conductance, Water Loss, and Water Content by Red-Winged Blackbird Embryos

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Abstract
This study evaluated the relations between eggshell conductance to water vapor ( ), daily water loss ( ), embryonic water content near pipping, and hatching success in red-winged blackbird eggs under conditions of natural incubation. All embryos hatched successfully over a 4.3-fold range in O. Eggs losing water within this range would be expected to lose between 7.4% and 33.0% of initial mass as water vapor during incubation. Some embryos hatched successfully from eggs losing as much as 43.5% of initial mass during incubation. All embryos would be expected to hatch from eggs with a varying over a 5-to 11.1-fold range, depending on altitude, and with water contents varying between 80% and 88%. The tolerance limits of red-winged blackbird embryos to variation in , , and water content substantially exceed the range of variation in these features found in untreated eggs under natural conditions of incubation and do not appear to vary significantly with altitude between 1,600 and 2,900 m. These embryos are substantially more tolerant to variation in gaseous flux during incubation than previously anticipated.