Respiratory Gas Exchange and Growth of Bonin Petrel Embryos

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Abstract
The constraints placed upon diffusive gas exchange by the eggshell, and parameters of embryonic respiration were examined in naturally incubated eggs of the Bonin petrel on Sand Island, Midway. The incubation period of the Bonin petrel egg was 49 days, or 184% of the predicted value based on egg mass; this is relatively longer than in larger members of the order. A low eggshell gas conductance was matched by a low egg O₂ uptake ( ), resulting in air cell gas tensions ( , ) of 101 torr, , and 46 torr, , just prior to external pipping. Pre-external-pipping averaged 246 ml O₂ standard temperature and pressure, dry (STPD)·day⁻¹ External pipping (shell fracture) occurred at the eighty-eighth percentile of incubation and prior to internal pipping (penetration of the air cell). This adaptive pipping behavior attenuates the low O₂ and high CO₂ air cell gas tensions and allows O₂ uptake to increase to levels characteristic of avian hatchlings, free of the diffusive limitations imposed by a low eggshell gas conductance. The total amount of O₂ consumed during the 6-day pip-to-hatch interval (2.8 liters·O₂ STPD) was 50% of the total amount of O₂ consumed over the entire incubation period. The total O₂ cost per gram of initial egg mass (143 ml O₂ STPD·g⁻¹ egg), and the total energetic expenditure for embryonic development (4.21 kJ·g⁻O¹ hatchling tissue), are consistent with the hypothesis that the energetic cost of embryonic development increases with decreasing egg mass among Procellariiformes.