Modelling heat and mass exchange of buried avian eggs.

The eggs of the Megapodiidae are incubated while buried in a substrate with which they exchange heat and water. The eggs may be buried in sand or in a mound composed in part or totally of organic material. We have analyzed the heat and water exchange of these buried eggs by constructing egg heat and mass balances. The equations are used to examine changes in egg temperature and water exchange during incubation in different environments. The thermal conductivities of the substrates are likely to vary by a factor of 5 to 10, with sand having the greatest thermal conductivity and organic litter the smallest. We predict that eggs incubated in sand will increase in temperature by 1 degree C or less, whereas eggs incubated in organic material will increase in temperature by 4 degrees C or more. Mound temperatures should remain low (less than 35 degrees C) to prevent overheating of eggs and hatchlings. Eggs can be incubated in sand at higher temperatures with less risk of overheating. Egg water loss in mounds is likely to be variable depending on mound humidity and considerably greater than 0 even in very high humidities. We expect that the rate of water loss by the eggs will increase many fold during incubation because of the low thermal conductivity of the mound material and the consequent increase in egg temperature.