Estimation of Daily Energy Expenditure from Heart Rate and Doubly Labeled Water in Exercising Geese

We investigated whether daily O₂ consumption (V̇o2) could be predicted from heart rate (fH) in five exercising barnacle geese (Branta leucopsis) and compared the accuracy of this method with that of the doubly labeled water (DLW) method. The regressions of V̇o2 on fH, based on incremental speed tests, differed among individual birds. The O₂ pulse (i. e., V̇o2/fH) progressively increased with exercise level from 0.22 mL O₂ heartbeat⁻¹ during resting to an estimated 0.47 mL O₂ heartbeat⁻¹ during flight. Daily V̇o2, was generally underestimated (-3.9%) by (individual) resting O₂, pulses but overestimated (+8.4%) by linear regressions of V̇o2 on fH. However, it was wellpredicted (+0.8%) by the O₂ pulses appropriate for each exercise level When using relationships derived from the group of birds, the estimations were generally improved (-3.3% for resting O₂, pulse, -0.03% for appropriate O₂ pulse) but poorer (+13.6%) for the group linear regression. Some of these predictions were better than the estimation of daily CO₂ production (V̇o2) by the two-compartment model of the DLW method (average algebraic error of +0.9%). We conclude that fH can be used to estimate daily energy expenditure in birds accuratelyprovided that (1) its application is limited to the range of exercise levels in which fH has been calibrated against V̇o2 and (2a) V̇o2-fH relationships are determined for each individual bird or (2b) the fH measurements of several free-ranging birds are averaged. Heart rate can also be used to indicate within-day variation in energy expenditure.