The Eggs of the Anatidae: Conductance, Pore Structure, and Metabolism

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Abstract
The water-vapor conductance ( ) of the eggs of 61 species of birds of the family Anatidae is reported. The relationship between egg weight (W), incubation period (I), and conductance for these species is similar to that of the eggs of 15 orders of birds; the mean value of the conductance coefficient ( ) is 5.15 ± 1.13. Pore area, using electron microscopy, pore length, and the total number of pores per egg were measured to calculate water-vapor conductance according to Fick's law of diffusion. The mean difference between the calculated value and the value directly measured on the same egg was -10%. The rate of oxygen consumption near the end of incubation was determined for the eggs of 11 species. In general, the rate observed 2 days before pipping is lower than the rate observed 3 days and 1 day before pipping. The allometric relationship between egg weight and the rate of oxygen consumption ( ) 2 days before pipping is proportional to the 0.72 power of egg weight. The aircell gas tensions prior to pipping were either measured directly or calculated from the O₂ conductance and O₂ consumption. The mean partial pressures for O₂ and CO₂ for 11 species were 103 and 41 torr, respectively. These functional properties of Anatid eggs appear to fall in line with those described for bird eggs of taxonomically more diverse groups.