How might turbulence affect animal flight in a changing world?

The influence of wind on animal flight costs and flight decisions is well established. Far less is known about the effects of turbulence. Indeed, a mechanistic framework allowing researchers to predict the costs and consequences of turbulence for flapping flight is lacking. This is a notable knowledge gap, as turbulence is ubiquitous within the natural flight environment, and its characteristics and distribution are changing across the spectrum of animal flight heights as a result of, for example, land use change and increasing atmospheric instability. Here, I briefly assess naturally occurring and anthropogenic drivers of turbulence before considering how turbulence affects the metabolic costs of flight and how animals might respond in the wild. Turbulence has a measurable effect on flight costs when eddy diameter is comparable to the wingspan. The few metabolic data on this suggest that turbulence can increase flight power by 25-100%. The ability to meet the costs of turbulence should decrease with increasing body mass, because of the negative relationship between available power and mass. Larger flapping fliers may therefore show stronger behavioural responses to turbulence. Consistent with this, waterbirds and large seabirds show marked avoidance of offshore wind farms, but this has yet to be analysed in relation to turbulence. Overall, the integration of laboratory and field approaches should provide new insight into the conditions animals avoid, the associated costs (according to eddy size, velocity and flight morphology) and the implications for flight in changing airscapes.