Validation of quantitative magnetic resonance as a non-invasive measure of body composition in an Australian microbat

Body composition (the total amount of fat mass, lean mass, minerals and water that constitute the body) is an important measure for understanding an animal's physiology, ecology and behaviour. Traditional measures of body composition require the animal to either be placed under anaesthetic, which is invasive and can be high-risk, or be euthanised, preventing the ability to perform repeated measures on the same individual. We aimed to validate quantitative magnetic resonance (QMR) as a non-invasive measure of body composition by comparing QMR scans with chemical carcass analysis (CCA) in Gould's wattled bats (Chalinolobus gouldii). In addition, we compared a commonly used microbat body condition index (residuals of mass by forearm length) to CCA. We found that QMR is an accurate method of estimating body condition in Gould's wattled bats after calibration with regression equations, and the condition index could accurately predict lean and water mass but was a poor predictor of fat mass. Using accurate, non-invasive, repeatable measures of body condition may have important implications for ecological research in the face of changing environments.