Incubation Water Loss in King Penguin Egg. I. Change in Egg and Brood Pouch Parameters

Water loss and thermal relations of the king penguin egg and its microenvironment (brood pouch) were studied under natural conditions. Despite the low ambient humidity (Pamb = 6.8 Torr, Tamb = 6.9° C), diffusive water loss during the prolonged 53-d incubation was within the range for other bird eggs, being 13% of the mean 302-g initial egg mass. Daily water loss increased throughout incubation to 1.54 times the initial value, while the low initial water vapor conductance of the shell, Gsb = 28.1 · mg · (d · Torr)−1, increased by 16%. The increase in Gsb was correlated withpartial loss of the organic shell cover by contact with the moist brood pouch. Brood patch temperature remained constant at 38. 2° C, while egg core temperature increased throughout incubation by 3°C The accompanying decrease in the vertical gradient of temperature inside the egg was explained mainly by a warming from 28° to 35°C of the foot region in contact with the shell. The influence of the embryo on egg temperature increase appears secondary, as the fertile eggs at day 50 had a core temperature only 0.7°C higher than unfertile eggs.