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P. Mbaabu Mathiu, William R. Dawson, G. Causey Whittow, Thermal Responses of Late Embryos and Hatchlings of the Sooty Tern, The Condor: Ornithological Applications, Volume 96, Issue 2, 1 May 1994, Pages 280–294, https://doi.org/10.2307/1369314
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Abstract
Oxygen consumption (VO2) and body temperature (Tb) of young Sooty Terns (Sterna fuscata) were measured during late incubation and in the first 24 hr after hatching at ambient temperatures (Ta) between 28° and 38°C and between 15° and 43°C, respectively. Evaporative cooling by hatchlings at Ta of 36°-43°C was also measured. Significant increases in embryonic metabolic level occurred between external and internal pipping and between internal pipping and establishment of a pip hole. However, despite the improving access to oxygen produced by these events, VO2 and Tb both varied directly with Ta in an ectothermic pattern throughout the final stages of incubation. A capacity for sustained endothermy only became apparent in hatchlings. Their VO2 varied inversely with Ta between 27.5° and 36°C to an extent indicating a modest capacity for regulatory thermogenesis. This served to maintain Tb above 35°C in this range of Ta. The apparent abruptness of the appearance of this regulatory capacity after hatching suggests that emergence from the physical confinement of the egg could be an important proximate factor in the establishment of endothermy in this semi-precocial species. Hatchling Sooty Terns underwent a progressive fall in Tb with declining Ta below 27.5°C. On the other hand, they appeared quite proficient at evaporative cooling with increasing Ta between 36° and 43°C.
