Respiratory Gas Exchange and Growth of White Tern Embryos

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Abstract
The parameters of respiratory gas exchange and growth in white tern (G. alba) eggs were examined during natural incubation. The O2 consumption of eggs (.ovrhdot.MO2) reached a plateau on day 32 of the 35.5-day incubation period resulting in an average .ovrhdot.MO2 of 159 ml O2 STPD [stardard temperature and pressure, dry] .cntdot. day-1 immediately prior to external pipping, and air cell gas tensions of 100 torr for O2 and 49 torr for CO2. .ovrhdot.MO2 increased rapidly during the 5.2-day pip (star fracture)-to-hatch interval, achieving an .ovrhdot.MO2 of 470 ml O2 STPD .cntdot. day-1 in hatchling chicks. The level of pre-pipping .ovrhdot.MO2 appears to be adaptive to prolonged incubation and is related to the extent to which the incubation period deviates from the expected value based on initial egg mass. The mean pre-external pipping daily water loss (.ovrhdot.MH2O) was 78.7 mg .cntdot. day-1 but increased to 275 mg .cntdot. day-1 in externally pipped eggs, yielding a 17.5% total fractional mass loss over the entire incubation period. The pre-pipping cost of prolonged semi-precocial development, calculated by indirect calorimetry, was 2.71 kJ/g yolk-free embryonic tissue. The total energy expenditure for embryonic development was 3.32 kJ/g of hatchling tissue.