Simple, rapid, and non-invasive measurement of fat, lean, and total water masses of live birds using quantitative magnetic resonance

An ideal technology for non-invasive analysis of body composition should provide highly precise and accurate direct measurements of fat, lean mass and total water of non-anaesthetized subjects within minutes. We validate a quantitative magnetic resonance (QMR) body composition analyzer for birds using House Sparrows (Passer domesticus), European Starlings (Sturnus vulgaris), and Zebra Finches (Taeniopygia guttata). Subjects were scanned awake for three replicate scans of 1.5-3.5 min, and results were compared to gravimetric chemical analysis. Coefficients of variation were a parts per thousand currency sign3% for dry fat, wet lean mass and total water. Accuracy of the raw QMR data for fat and total water were high (relative errors a parts per thousand currency sign +/- 12.5 and a parts per thousand currency sign +/- 4%, respectively), but wet lean mass was significantly biased because QMR does not detect structural tissues. Calibration against gravimetric chemical analysis removed bias and improved accuracy; relative errors were +/- 6-11% for fat, +/- 1-2% for wet lean mass, and +/- 2-4% for total water. QMR is field-portable when transported in a temperature-controlled trailer, and can be used to study fuel storage and body composition dynamics during migration, reproduction, nestling growth, or wintering. In the laboratory, QMR can be used for longitudinal studies of birds under photoperiod, endocrine or other manipulations. Measurements taken before and after metabolic challenges, such as flight in a wind tunnel, make it possible to calculate energy costs, fuel selection and changes in hydration. QMR should find wide application in field and laboratory studies.