Nest microclimate and incubation water loss of eggs of the African ostrich (Struthio camelus var. domesticus).

The microclimate of the nest and the rates of egg water loss were studied at weekly intervals throughout the 41-day incubation period in six ostrich nests. Overall mean values were a central egg temperature of 34.9 degrees C associated with saturation vapor pressure of 42 torr, a mean nest vapor pressure of 11 torr, and an ambient vapor pressure of 8.4 torr. The egg water loss increased from 4,000 to 4,800 mg X day-1 over the incubation period, and the total water loss was equal to 13.2% of the initial egg mass of 1,368 gm. The mean rate of water loss (4,403 mg X day-1) divided by the water vapor conductance of the shell (147 mg X day-1 X torr-1) equals 30 torr. When this value is added to the nest vapor pressure of 11 torr, it predicts an egg saturation vapor pressure of 41 torr, similar to that derived from the central egg temperature.