Gilbert S. Grant

Metabolic cost of incubation in the Laysan albatross and Bonin petrel

1. Oxygen consumption and carbon dioxide production were measured in resting and incubating Laysan albatrosses and Bonin petrels on Midway Atoll in the north central Pacific Ocean. 2. Incubation metabolism within the thermal neutral zone is less than or equal to resting metabolism in the albatross and petrel. 3. The respiratory quotients (0.64-0.72) during the long fasts indicate fat metabolism. 4. The estimated fractional water content of the albatross and petrel do not change during incubation fasts because water loss is balanced by metabolic water production.

Respiratory Gas Exchange and Growth of Bonin Petrel Embryos

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 (Ṁo2), resulting in air cell gas tensions (PaO2, PaCO2) of 101 torr, PaO2, and 46 torr, PaCO2, just prior to external pipping. Pre-external-pipping Ṁo2 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.

Nestling metabolism and growth in the black noddy and white tern

The White Tern (Gygis alba) and Black Noddy (Anous minutus) are two tropical charadriiform seabirds characterized by prolonged incubation of their eggs, slow embryonic growth, and a high total energetic cost of embryonic development (Whittow 1980, Pettit et al. 1981, Pettit and Whittow 1983). The present study was undertaken to ascertain if post-hatching growth was also slow and if the nestling period was prolonged in the two species. A long nestling period reduces the energy requirement of the chick (Ricklefs and White 1981) but may place an energetic burden upon breeding adults. To evaluate this possible energetic constraint in the Black Noddy, the oxygen consumption of the chick was measured to estimate the total energy cost of maintenance activities.

Water Loss from Eggs of the Great Frigatebird

Abstract The natural incubation period of Great Frigatebird (Fregata minor) eggs reported in the literature (55 days) was 74% longer than the value predicted from initial egg mass (89.1 g). The long incubation period was associated with a low daily water loss (213.5 mg/day) from the eggs and few pores in the eggshell (4,643 pores/egg). The initial event in the pipping process, which represented 7.2% of the duration of the incubation period but accounted for 24.9% of the total water loss from the egg, was a star-shaped fracture of the shell which increased water loss from the egg and persisted for several days before hatching was complete. These characteristics of the eggs of the Great Frigatebird are contrasted with those from the Red-footed Booby (Sula sula), the only other altricial, pelecaniform seabird with a long incubation period, for which data are available.