Inferring Whole-Organism Metabolic Rate From Red Blood Cells in Birds

Metabolic rate is a key ecological variable that quantifies the energy expenditure needed to fuel almost all biological processes in an organism. rates are typically measured at whole-organism level (woMR) with protocols can elicit stress responses due handling and confinement, potentially biasing resulting data. Improved, non-stressful methodology would be especially valuable for measures of field metabolic rate, which free-living individuals. Recently, techniques measure cellular (cMR) mitochondria blood cells have become available, suggesting blood-based cMR proxy organismal aerobic performance. Aerobic metabolism actually takes place mitochondria. Quantifying from samples offers several advantages such as direct estimates minimized disturbance To our knowledge, hypothesis correlates woMR has not yet been directly tested. We red captive great tits ( Parus major ), first during their morning activity period second after subjecting them 2.5 h day-time respirometry protocol quantify woMR. predicted decrease individuals transitioned active resting state. In two we also assessed circulating corticosterone concentrations determine perceived From traces extracted initial final test positive correlation measures, while accounting concentrations. Indeed, declined measurement. Furthermore, were positively related had relatively low displayed little locomotor throughout respirometry. By contrast, covaried negatively birds increased levels substantially. Our results show cell represents when do display signs stress, i.e., either before increases hormonal or behavioral parameters occurred they abated. This method tool obtaining data repeatedly findings highlight importance individual measuring any level.