Moving beyond body condition indices as an estimate of fitness in ecological and evolutionary studies

Summary Body condition indices, measures of body ‘plumpness’ or mass relative to frame size, are often used as a proxy for lipid reserves or fitness‐related traits of animals and assumed to be positively related to fitness. The quantification and analysis of body condition indices has been the subject of debate for decades. Here, we summarize three additional concerns with the use of body condition indices. First, body condition index is often...