Ventilatory Oxygen Extraction in Relation to Ambient Temperature in Four Antarctic Seabirds

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Abstract
We tested the hypothesis that at low ambient temperatures ( ) birds reduce ventilatory heat loss by increasing ventilatory oxygen extraction ( ). We examined relationships between , body temperature, oxygen consumption ( ), carbon dioxide production ( ), evaporative water loss ( ), respiratory frequency, tidal volume ( ), minute volume, and , in four species of Antarctic marine birds ranging in body mass from 33-4,915 g The factorial increases in ranged from 1.8 to 5.2 between the lower critical temperature ( ; 10° -30° C, depending on species) and a of -23°C. The respiratory exchange ratio ( ) did not change with . The was independent of between 10° and 30° C in kelp gulls and giant petrels but was positively correlated with between 10° and 35° C in Wilson's storm-petrels and between 10° and 30° C in South Polar skuas. Thermal conductance (C) was minimal at of 10° or 20° C depending on the species and was constant and low at below this minimum. In all four species C increased significantly at high . In storm-petrels, gulls, and skuas, the increase in , resulting from a change in from down to -23°C was accommodated mainly by increasing . In contrast, in giant petrels the increase in resulting from a change in from down to -23°C was accommodated mainly by increasing , and the increase in was of secondary importance. Our data suggest that increasing , as a means of reducing ventilatory heat loss is not a general phenomenon in cold-adapted birds.