Development of Thermoregulation in Three Species of Tropical Seabirds

Abstract

'The development of thermoregulation was studied in three species of tropical seabirds: Sooty Tern (Sterna fuscata), Brown Noddy (Anous stolidus) and the Wedge-tailed Shearwater (Puffinus pacificus) . late prehatichinq stages (unpipped, externally pipped, internally pipped and pip-holed eggs) of eggs, and hatchlings were subjected to small decrements in ambient temperature (Ta) and their oxygen consumption (V02) and body temperature ('Ib) measured. Evaporative water loss and respiratory frequencies of hatchlings at higher temperatures were also measured together with musc.Iemass, downmass, and length (thickness). All the egg developmental stages showed a direct coupling of . their V02 and 'Ib to ambient temperatures. On the other hand the hatchlings showed a homeothermic of metabolic response to Ta. The increase in V02 below the thermoneutral zone peaked and then fell precipitously with further reduction of Ta. Hatchling rectal temperatures (Tre) increased slowly with Ta between the temperature at which this metal:x>lic decline began and the upper limit of thermoneutrality. 1\rx:Jve the thermoneutral zone, Tre increased at a faster rate but the Sooty Tern and Brown Noddy hatchlings maintained their Tre below Ta above 4°0C. Evaporative water loss and respiratory rates increased dramatically above the thermoneutral zone. v No homeothermic response was observed. during the late prehatching, but hatchlings showed a homeothermic response qualitatively similar to that of the adults. 'Ihe hatching process seems to be crucial for this transition and the probable underlying chances are d; scussed, Hatchling Sooty Terns p:>SSeSS the best overall thermoregulatory abilities arrong the three species. Hatchling BraNn Ncx:kiiesthenroregulate better during heat stress than cold stress, whereas the Shear water hatchlings do the reverse. Using their therm:::xJenic capacities and the difference between their Lower'critical . temperature am the Ta at which peak V02 occurred, the hatchlings are ranked from least to most semi precocial in the following order: Brown noddy, sooty Tern am Wedge-tailed Shearwater.