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

Abstract

We tested the hypothesis that at low ambient temperatures (Ta) birds reduce ventilatory heat loss by increasing ventilatory oxygen extraction (Eo2). We examined relationships between Ta, body temperature, oxygen consumption (V̇o2), carbon dioxide production (V̇co2), evaporative water loss (ṁH2O), respiratory frequency, tidal volume (VT), minute volume, and Eo2, in four species of Antarctic marine birds ranging in body mass from 33-4,915 g The factorial increases in V̇o2 ranged from 1.8 to 5.2 between the lower critical temperature (Tlc; 10° -30° C, depending on species) and a Ta of -23°C. The respiratory exchange ratio (V̇co2/V̇o2) did not change with Ta. The ṁH2O was independent of Ta between 10° and 30° C in kelp gulls and giant petrels but was positively correlated with Ta 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 Ta's of 10° or 20° C depending on the species and was constant and low at Ta's below this minimum. In all four species C increased significantly at high Ta's. In storm-petrels, gulls, and skuas, the increase in V̇o2, resulting from a change in Ta from Tlc down to -23°C was accommodated mainly by increasing VT. In contrast, in giant petrels the increase in V̇o2 resulting from a change in Ta from Tlc down to -23°C was accommodated mainly by increasing Eo2, and the increase in VT was of secondary importance. Our data suggest that increasing Eo2, as a means of reducing ventilatory heat loss is not a general phenomenon in cold-adapted birds.