Microclimate of ostrich nests: measurements of egg temperature and nest humidity using egg hygrometers

Summary

• 1. A method is described for determining the temperature of fertile and infertile eggs of the African Ostrich, the absolute humidity of the nest and ambient air during 41 days of incubation without recourse to direct thermometry or relative humidity sensor. These values are calculated from weekly determinations of mass changes of a diffusion hygrometer made from an ostrich eggshell, and eggs in the nest, some of whose shell conductance to water vapor had been previously established.

• 2. During the incubation period the absolute nest humidity remained relatively constant at a mean value of 13.2 Torr and is maintained 4.7 Torr above the ambient humidity. The saturation water vapor pressure of fertile (but not of infertile) eggs gradually increases from 41 to 47 Torr because of the rise in egg temperature from 34.5 to 37.1°C at the end of incubation. Infertile eggs remain at 35.0°C.

• 3. Because of the increase in saturation vapor pressure of fertile eggs during the last half of incubation, the water vapor pressure difference between the egg and the nest air increases. This change accounts for the proportional change in egg water loss which increases from 4.3 to 5.0 g d⁻¹ at the end of 41 days.