The regulation of water loss from the eggs of the red-footed booby ( Sula sula)

Abstract

1. 1. The red-footed booby is a tropical seabird that does not develop a brood patch, incubating its eggs instead with its large webbed feet. This was found to be associated with a relatively high egg temperature (36.4°C) and also a high value for the water-vapor pressure (26.96 torr) in the microclimate of the incubated egg. 2. 2. The “relative mean growth rate” (freshly-laid egg mass/incubation period) of Ar and Rahn (1985) was a good basis for predicting the daily rate of water loss from the egg, the measured value (174.6 mg/day) representing 96.3% of the predicted value. 3. 3. The water-vapor conductance of the egg shell was less well predicted by the relative mean growth rate. This was attributed largely to the thick chalky shell of the red-footed booby's egg. 4. 4. The data obtained in the present study provide additional support for the belief that there is a constant relationship between the cross-sectional area of the pores in the eggshell, through which water vapor diffuses, and the length of the pores, in all eggs.