Heart rates (fh) and rates of oxygen consumption (V(dot)O2) were measured in eight black-browed albatrosses (Diomedea melanophrys) when walking on a treadmill, with the aim of using fh to predict V(dot)O2 in free-ranging albatrosses. The resulting relationship between the variables was: V(dot)O2 (ml min-1) = [0.0157fh (beats min-1)]1.60, r2=0.80, P<0.001. In addition to the calibration procedure, six of the albatrosses were injected with doubly labelled water (DLW), and fh and V(dot)O2 were monitored continuously over a 3 day period while the birds were held in a respirometer. During the 3 day period, the birds were walked for up to 3&shy;4 h day-1 in bouts lasting approximately 0.5 h. The heart rate data were used to estimate the metabolic rates of these birds using the above regression. Estimates of metabolic rate derived from fh, DLW and respirometry did not differ (ANOVA; P=0.94), primarily because of the variance between individual birds. There was also no significant difference between the different estimates obtained from the different equations used to calculate energy expenditure from the DLW technique (ANOVA; P=0.95). Mean estimates of V(dot)O2 from fh under active and inactive conditions differed from measured values of V(dot)O2 by -5.9 % and -1.7 % respectively. In addition, the estimates of V(dot)O2 from fh at different walking speeds did not differ significantly from the measured values. It appears that, in the black-browed albatross, fh is as good a predictor of the mean metabolic rate of free-ranging birds as DLW or time&shy;energy budgets combined with either respirometry or DLW. However, the method should be applied to as many individuals and as many instances of a particular behaviour as possible. The heart rate technique offers potential for much more detailed analyses of the daily energy budgets of these birds, and over much longer periods, than has previously been possible.

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