Embryonic Respiration and Growth in Two Species of Noddy Terns

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Abstract
Embryonic oxygen consumption, gas transfer, and growth were measured during natural incubation in the black (Anous tenuirostris) and brown noddy (A. stolidus). The mean pre-external pipping oxygen consumption ( ) among black noddy eggs was 184 ml O₂ STPD • day⁻¹ and occurred at a mean embryonic mass of 10.95 g on day 28 of the 35-day incubation period. Pre-external pip air cell gases in black noddy eggs were 98.5 torr for O₂ ( ) and 42.3 torr for CO₂ ( ). Hatchling black noddies (mean weight 16.80 g) consumed 524 ml O₂ STPD • day ⁻¹. Pre-external pip in brown noddy eggs averaged 283 ml O₂ STPD • day⁻¹ at a mean embryonic mass of 17.63 g on day 30-31 of the 36-day incubation period. Pre-external pip was 92.1 torr and , was 46.6 torr. Hatchling brown noddies (mean weight 28.52 g) consumed 690 ml O₂ STPD • day⁻¹. The characteristics of embryonic respiration and growth exhibited by black and brown noddies are typical of other seabird eggs with prolonged incubation. A low rate of pre-external pipping , a long pip-tohatch interval, a high cumulative oxygen consumption between external pipping and hatching, and a high energetic cost of embryonic development are common features in the two species.