Frailty: measurement and utility in avian studies

Here, I discuss the utility of the concept of frailty, which is widely used in human gerontology, for studies of ageing in wild animals and birds in particular. Frailty indices generally aim to capture the age‐specific health status of individuals via relatively simple measures of whole‐organism performance. I discuss why we might find frailty indices useful in studies of animal life histories, environmental factors and ageing, and how frailty might be usefully measured in birds by different methods. I also discuss limitations and caveats.