Research overview: doubly labelled water validation of accelerometer energetics

To trust accelerometer-derived energy estimates, researchers validate them against independent physiological measures, and the doubly labelled water method is a gold standard for field metabolic rate. This overview describes how isotopically labeled water, sampled before and after a period, yields total carbon-dioxide production and thus energy expenditure, which can be compared with simultaneous accelerometer and metabolic-chamber data. Such validation underpins confidence in scaling biologging proxies to free-ranging cats. The overview covers the practical difficulty of applying these methods to large, dangerous carnivores, which is why much calibration relies on trained captive animals, and the resulting uncertainty when extrapolating to the wild. Rigorous cross-validation is what separates speculative energy budgets from defensible quantitative carnivore energetics.