Water Loss from Laysan and Black-Footed Albatross Eggs

Daily mass loss (ṀH2O) of 75 black-footed albatross eggs averaged 707 mg · day⁻¹ ± 12 (SE) and 674 mg · day⁻¹ ± 9 (SE), for 98 Laysan albatross eggs. Daily mass loss increased during natural incubation in both species and is described by the equation ṀH2O = 6.585 time + 537.97, no. = 183, r = .651 for the egg of the Laysan albatross. Fractional water loss, including the increase due to shell fracture and pipping, amounted to 16.1% in the black-footed albatross and 16.0% in the Laysan albatross. Nest vapor pressure averaged 17.3 torr ± 0.2 (SE) for 109 black-footed albatross nests and 19.1 torr ± 0.2 (SE) for 262 Laysan albatross nests. Ambient vapor pressure averaged 13.7 torr ± 0.4 (SE), no. = 56, and influenced changes in nest vapor pressure. Central egg temperature increased from 34.2 C to 37.3 C and 33.7 C to 36.3 C in Laysan and black-footed albatross, respectively, during the course of incubation. The increase was due to metabolic heat production by the embryo. The increase in egg vapor pressure (due to increased egg temperature) resulted in an increasing gradient (ΔPH2O) between egg and nest vapor pressure during the course of natural incubation. The increasing vapor pressure gradient was responsible for the increased rate of daily water loss. Water vapor conductance did not increase during natural incubation (ṀH2O/ΔPH2O), and field-determined values agreed well with laboratory-determined values. Black-footed albatrosses tended to "ventilate" the nest half as frequently as did Laysan albatrosses. Prolonged incubation was associated with relatively low values for the daily water loss from the egg, water vapor conductance of the shell, and functional pore area. However, these trends are not as pronounced in the larger albatrosses as in the smaller shearwaters and petrels.