Thermoregulation in Antarctic fulmarine petrels

We measured resting metabolic rates at air temperatures between ca. -5 and 30 degreesC in snow petrels (Pagodroma nivea), cape petrels (Daption capense), Antarctic petrels (Thalassoica antarctica), and Antarctic fulmars (Fulmarus glacialoides). We measured seven age classes for each species: adults, and nestlings that were 3, 8, 15, 28, 35, and 42 days old. Basal metabolic rate (BMR) and thermal conductance (C) of adults averaged, respectively, 140% and 100% of values predicted allometrically for nonpasserine birds. Minimum metabolic rates of unfasted nestlings aged 15-42 days averaged, respectively, 97% and 98% of predicted adult BMR in Antarctic petrels and snow petrels, Versus 119% and 126% of predicted in Antarctic fulmars and cape petrels. Nestlings of the southerly breeding snow petrel and Antarctic petrel were relatively well insulated compared with nestlings of other high-latitude seabirds. Adult lower critical temperature (TI,) was inversely related to body mass and averaged 9 degreesC lower than predicted allometrically. As nestlings grew, their T-1c decreased with increasing body mass from ca. 14 to 22 degreesC (depending upon species) at 3 days of age, to -4 to 8 degreesC when nestlings attained peak mass. Nestling T-1c subsequently increased as body mass decreased during pre-fledging weight recession. Nestling T-1c was close to mean air temperature from the end of brooding until hedging in the three surface nesting species.